Simulated Stress-strain Curves Research Articles

Towards accurate prediction of the dynamic behavior and failure mechanisms of three-dimensional braided composites: A multiscale analysis scheme

In this paper, a dynamic multiscale model is proposed for three-dimensional four-directional (3D4D) braided composites, considering the effects of strain rate and shear enhanced failure mechanism. The strain rate-dependent constitutive models are established for both resin and yarns. The accuracy of the yarn model is validated by comparing the simulated stress-strain curves with the experimental results obtained from the Split Hopkinson Pressure Bar (SHPB) tests with various strain rates. The shear enhancement coefficient of the yarn is determined from the failure envelopes with a discussion of crack propagation angles. The results show that, based on the calculated microscale properties, the mesoscale model accurately predicts both the longitudinal and transverse compressive strain-stress behavior of 3D4D braided composites at different strain rates. A comparative analysis reveals that the shear-enhanced failure model achieves a better prediction compared with other counterparts, such as Hashin-Rotem and Tsai-Wu Models. The proposed dynamic multiscale scheme for 3D braided composites is an efficient and accurate tool to characterize their multiscale features and strain rate-dependent behavior.

Numerical simulation of microstructural failure of natural fibre–hydrogel composites

In this article, we conduct a numerical simulation to investigate the failure mechanism of natural fibre–hydrogel composites under tensile deformation and swelling. Firstly, a physical-based constitutive model is chosen to describe the deformation of the hydrogel matrix. Concurrently, a macroscopic phenomenological hyperelastic constitutive model, incorporated into the material database of Abaqus, is employed to describe the mechanical responses of natural fibres. Then, we implement the model for a numerical analysis. The material parameters of the model for the hydrogel matrix and fibres are determined by a trial-and-error method from the experimental curves of pure hydrogel and fibres; the numerically simulated stress–strain curve of the composites is compared with the experimental one to verify the effectiveness of the simulation. Subsequently, several numerical analyses are performed to discuss the failure mechanism of hydrogel composites caused by the microstructural features of fibres. The findings revealed that fibre protrusion, fibre orientation deviation, and interface strength significantly affect the local failure of the composites during tensile deformation and swelling; the composites’ strength and toughness mainly depend on the cooperation of various microstructural features. These results provide valuable insights into the design of fibre–hydrogel composites.

Dynamic compression intrinsic relationship of W-Ni-Fe-Mn alloys based on J-C modeling

Dynamic compression tests were performed on the sample alloys by using a detached Hopkinson compression bar with a diameter of 14.5 mm caliber for the kinetic behavior of W-Ni-Fe alloy and W-Ni-Fe-Mn alloy materials in the erosion process. The true stress-true strain curves of the two sample alloys were fitted based on the JC eigenstructure model, and the eigenstructure relationships of the two alloys were finally obtained. The obtained constitutive equations were then used to dynamically compress the specimens by using LS-DYNA dynamics software, and the simulated true stress-strain curves of the two alloys at various strain rates agreed well with the experimentally obtained curves, allowing them to be used for simulation calculations under impact loading. When compared toW-Ni-Fe alloys, the dynamic mechanical characteristics of alloys with Mn addition are greatly improved.

Texture evolution and stress formation behaviour during tensile deformation using crystal plasticity finite element method

In this work, a three-dimensional crystal plasticity (CP) model was constructed to study the texture evolution behaviour and stress distribution of AA2024 alloy under uniaxial tensile conditions. After parameter calibration, the accuracy of simulated stress–strain curve reached 98.82%, and with good convergence. It was found that the {111} plane dots of Brass in (111) pole figure predominantly prolong at an angle of approximately 35.8° with respect to the RD, while those of Copper, S, Goss and Cube scatter towards almost all directions by the way in a circular augmentation. Moreover, it was revealed that Brass orientation is more conducive to alleviating stress during deformation process, while Copper is the least effective. The situations for Cube and Goss orientations are similar.

Experimental study and simulation of workability and compressive performance of SCC with high-volume mineral admixtures

Using industrial waste such as fly ash and silica fume to substitute most of the cement to prepare self-compacting concrete can not only greatly reduce the cement consumption, but also improve the resource utilization of solid waste powder, which is conducive to cost reduction and environmental protection. In this paper, the fly ash (FA) and silica fume (SF) replacement ratio of 40%, 50% and 60% was adopted to produce self-compacting concrete with high-volume mineral admixtures (HVMA-SCC). The slump flow test, L-box test and compression test were conducted, and the effect of different high replacement ratio on the workability, compressive performance and stress–strain relationship of HVMA-SCC were analyzed. The experimental results showed that when the total content of mineral admixtures was the same, an increase in SF content was beneficial for the development of early compressive strength. Under the same SF dosage, the larger the FA dosage, the faster the strength development rate, which was conducive to the sustained growth of HVMA-SCC strength in the later stage. Moreover, a stress–strain calculation model of HVMA-SCC was proposed based on damage theory. Besides, the workability and compression tests were simulated with the discrete element method (DEM). The results showed that the simulated stress–strain curves were in good agreement with experimental curves, and the mesoscopic failure characteristics of HVMA-SCC were analyzed from the development of cracks, stress conditions, and failure modes.

Influence of Ti particle sizes on microstructure and mechanical behaviors of AZ91-Ti composites under different loading paths

Magnesium (Mg) matrix composites are recognized as the most promising light structural materials and have been extensively investigated, but they still suffer from a relatively low ductile nature which seriously affects their further development. Herein, the Mg–9Al–1Zn (AZ91) Mg matrix composites with different sizes of Ti particles reinforcement can be obtained via hot pressed sintering followed by hot extrusion. The microstructure demonstrated that the interfacial region is consisted of Mg17Al12 and Al-rich phase. Uniaxial tensile experiments revealed that the AZ91-Ti (particle size of 15 μm) composite achieves the optimal comprehensive mechanical properties, and the corresponding yield strength (YS), ultimate tensile strength (UTS), elongation (EL) of the composite can reach the high values of 210 MPa, 310 MPa, 15.5%, respectively. Moreover, with the decrease of Ti particle size, grain refinement and the strong interfacial bonding between Ti particles and Mg matrix render as-prepared the composites exhibited outstanding mechanical properties. Ti reinforcement particles of appropriate size can alleviate the plastic strain accumulation during the tensile and compressive cyclic loading, so that the excellent ductility of the composite is obtained. Constitutive relation of AZ91-Ti composites in this experiment can be derived from the nonlinear elastic relation. The simulated stress-strain curves of the composites reinforced by Ti particles with different sizes are consistent with the experiment.

A DEM parameters calibration method for three-dimensional model of the lunar rock based on the approximate model

The development of an accurate rock discrete element model is essential for modeling core drilling in the lunar environment. However, most of the microscopic parameters of the discrete element model cannot be determined directly by tests. Consequently, a rapid calibration method for microscopic parameters was developed, combining an approximation model, multiple objectives with particle swarm optimization algorithm (MOPSO), and orthogonal experimental design (OED). Range analysis and variance analysis were conducted to investigate the sensitivity of these parameters. Through this approach, the optimal solution for microscopic parameters was obtained to align with the mechanical characteristics of lunar rock simulant, providing a foundation for rock core drilling. The results demonstrate a high level of agreement between the simulated stress-strain curves and the test results. The deviation between the mechanical strength parameters and actual test values was found to be less than 5%, confirming the effectiveness and rationality of the proposed parameter calibration method. This method holds significant potential for widespread application in calibrating the parameters of discrete element models for rock materials.

An insight into the creep-fatigue damage localization in welded joints based on crystal plasticity finite element method

In the present work, a numerical simulation based on the crystal plasticity finite element (CPFE) method is conducted to capture the different mechanical responses and damage in different micro areas of the P92 steel welded joint at 650 °C. A robust Matlab-Abaqus-Python interactive parameter optimization procedure is proposed to identify the constitutive parameters for heat affected zone (HAZ). Good agreement between experimental and simulated stress–strain curves verifies the accuracy of the present approach. Three fatigue indicator parameters are incorporated into the CPFE to capture the damage distribution under low cycle fatigue (LCF) and creep-fatigue interaction (CFI) loadings. The damage accumulation at grain boundaries is observed in the FE simulation. The damage captured by the simulation under both LCF and CFI loadings shifted from HAZ to base zone.

Time-dependent virtual crack model of rock with application to slope stability

Time-dependent deformation of rock involves the continuous to discontinuous deformation of joints, cracks, holes, and other defects under long-term stress conditions. Thus, it is of great significance to investigate the correlation between internal crack propagation in rock and external time-dependent damage and failure of rock to better understand the long-term stability of engineering rock mass. Here, we put forward a time-dependent virtual crack model to achieve the entire continuous-discontinuous time-dependent deformation progress of rock from the microscopic to the macroscopic scale. Simulated stress-strain curves for granite, including the mode of failure (axial splitting and Brazilian splitting), agree well with experimental data. We also used the virtual crack model to study the stability of one of the slopes of the Xiaowan Hydropower Station (China). The simulation results indicate that the weakly disturbed zone is the potential sliding surface, and that the deformation of the slope is similar to in-situ measurements. In the model, the vertical displacement decreased by 500 mm in 180 days and the axial strain rate decreased from 25 mm/d to zero, suggested that the slope is currently stable.

The effects of microstructural parameters on the tension-compression mechanical behavior of extruded Mg-XY rods using crystal plasticity finite element modeling

In the present study, the effects of rare earth element Y, texture intensity, and grain size on the tension-compression mechanical behavior of extruded Mg-XY(X = 0–3, wt pct) rods were investigated using improved phenomenological crystal plasticity. To this end, finite element modeling of a three-dimensional representative volume element (3D-RVE) was employed to consider the effects of microstructural parameters. Subsequently, the computational modeling approach was validated with the experimental data to assess the reliability of predictions of the responses of a polycrystalline aggregate. Afterward, the validated computational modeling was employed to predict the mechanical behaviors of extruded Mg-XY (X = 0–3, wt pct) by considering the role of slip/twinning activities during deformation. The results showed that the Y addition significantly improved the yield strength, ultimate strength, and ductility. Examination of the deformation modes activities indicated that the basal slip activity of extruded Mg-XY (X = 1–3, wt pct) is higher than that of extruded pure Mg due to the formation of non-basal texture components, which hindered the twinning activation. Increasing the Y content further reduced the suppression of tensile twinning activity. Therefore, the weak tension–compression yield asymmetry of extruded Mg-XY (X = 1–3, wt pct) was mainly attributed to the reduced tensile twinning activity. The simulated stress-strain curves illustrated that texture weakening, and grain refining improved the mechanical behavior and reduced tension-compression yield asymmetry.

Numerical simulation and analysis of fully-grouted sleeve connection and two special points at elevated temperatures

Fire is one of the main objects of study at the cutting edge of the research on disaster prevention and mitigation in structures. In the event of a fire, the mechanical properties of the structural material will be significantly reduced, resulting in serious consequences. This paper simulates the tensile properties of sleeve grouting members at five different temperatures, to contribute to the research here. The simulated member stress-strain curves fit well with the corresponding experimental results. The paper introduces constitutive models of concrete, steel, and sleeve. Beyond that, a feasible finite element model of the grouted sleeve is proposed. Two special points’ (yield point, ultimate point) coordinate formulas which are related to different temperatures (25–1000 °C) are presented. It indicates the regularity of fully-grouted sleeve tensile force-displacement curves in various temperatures. Meanwhile, the research content provides the basis for further research on reinforcing bars spliced by grout-filled coupling sleeves.

Effects of the CuO additive nanoparticles on the internal strain homogenization and microstructure evolution in Ag-SnO2 composites

Stress concentration caused by reinforcements has very unfavorable effects on the metal matrix composites, which will inevitably induce localized strains and crack initiation. In this paper, an effective approach is presented to relieve stress concentrations near the reinforcements in metallic composites. The Ag-SnO2 contact materials with CuO additive are prepared by electroless plating combined with powder metallurgy method. The CuO nanoparticles in-situ formed on the SnO2 reinforcements are adopted to relieve local stress concentrations near the Ag/SnO2 interfaces and promote strain homogenization. The mechanical properties, deformation characteristics and microstructure evolution of the Ag-SnO2 composites without and with CuO additive are systematically studied by experiments and numerical simulations. The results show that the CuO nanoparticles formed on the surfaces of the SnO2 reinforcements dramatically improve the mechanical properties of the Ag-SnO2 composites, particularly the plasticity at a higher loading rate. The ultimate strength of the Ag-SnO2(CuO) tensile specimens is increased from 104 to 127 MPa, and the uniform elongation is increased by 83% compared with that without CuO. It is demonstrated that the dislocation tangle around the CuO nanoparticles effectively relieves the adverse effect of the stress concentration near the SnO2 and results in the strain homogenization in the Ag matrix. Furthermore, the damage evolution of the Ag-SnO2 composites without and with CuO nanoparticles is investigated by the Gurson-Tvergaard-Needleman (GTN) models under uniaxial tension. The error range of the simulated stress-strain curves is lower than 4%. The nucleation and growth of voids at the interfaces of the Ag-SnO2 composites are numerically simulated and discussed. This study provides a fundamental basis for developing novel high-performance metal matrix composites.

Numerical Modeling of Damage Caused by Seawater Exposure on Mechanical Strength in Fiber-Reinforced Polymer Composites.

Fiber-reinforced polymer composites are frequently used in marine environments which may limit their durability. The development of accurate engineering tools capable of simulating the effect of seawater on material strength can improve design and reduce structural costs. This paper presents a numerical-based approach to predict the stress–strain response of fiber-reinforced polymer composites exposed to different seawater immersion times, ranging from 0 to 900 days. A three-dimensional numerical model has been implemented using a static implicit finite element analysis along with a user-defined material (UMAT) subroutine. Puck’s failure criterion was used for ultimate failure analysis of the laminates, while Fick’s first diffusion law was used to predict the seawater absorption rate. Overall, the simulated stress–strain curves were close to those obtained experimentally. Moreover, the model agreed well with the experimental data regarding the maximum stress and the strain at failure leading to maximum errors lower than 9% and 11%, respectively. Additionally, the simulated strain fields agreed well with the experimental results measured by digital image correlation. Finally, the proposed procedure was also used to identify the most critical surfaces to protect the mechanical components from marine environments.

Hysteresis Behavior Modeling of Hard Rock Based on the Mechanism and Relevant Characteristics

The modeling of cyclic behavior in rock remains a challenge due to complex deformation characteristics. This paper studied the mechanical behaviors of granite samples under uniaxial cyclic loading and unloading through cyclic compression tests and acoustic emission (AE) monitoring. Then, a comprehensive body that consisted of an elastic element, plastic element, and friction element was proposed to describe the stress–strain relationship with respect to cyclic behavior, in which the friction element was connected in parallel with the serial combination of the elastic element and plastic element. Finally, the parameters of the proposed model were calibrated based on the mechanism analysis and backpropagation (BP) neural network. Results show that the behavior during unloading is primarily elastic and is accompanied by the obstruction of friction. During reloading, the behavior changes from elastic to elastic–plastic before and after the Kaiser point. The tangential modulus of the elastic element is dynamic in a linear positive correlation with elastic strain and a linear negative correlation with plastic strain; specifically, the elastic strain controls the variation process of the elastic modulus while the plastic strain determines the lower limit. The constitutive law of the plastic element is expressed by a logistic function, which means that the plastic strain increases in a trend of acceleration–deceleration. The friction element plays a major role in processing the massing effect, and the plastic element is prompted before the historical maximum stress, which reflects the ratcheting effect and Felicity effect. The reliability of the proposed constitutive model is confirmed by the comparison of the simulated stress–strain curves with the experimental curves.

Fracture behaviour of silver nanowire films during shear deformation

Silver nanowire films have a wide application prospect in flexible electronics, while it is a noticeable problem that the silver nanowires break due to the shear force under the mass production film cutting or extreme service conditions. In this paper, the shear fracture behaviour of silver nanowire films with different structural parameters was studied under the extreme shear failure tests. The load–displacement curve was obtained from the nano-indentation test, while the hardness H, the elastic modulus E and the plastic properties represented by the ratio of H 3/E 2 of silver nanowire films with different diameters and thicknesses were calculated. On the other hand, based on the load–displacement curve, the stress–strain curve can be obtained through the finite element method simulation. The plastic properties can also be judged by the lower limit of yield strength from simulated stress–strain curve. Combined with characteristic crack propagation range, the relationship between plasticity and shear fracture was found, which was further disclosed by in-depth microstructure analysis. The results show that the better the plasticity of silver nanowire films, the stronger the resistance to shear fracture.

Full-range stress-strain relation of stainless-clad bimetallic steel: Constitutive modelling

Stainless-clad (SC) bimetallic steel possesses promising application potential in civil and structural engineering due to a favourable combination corrosion resistance and load-bearing capacity. Nevertheless, the stress-strain models proposed in existing researches are solely suitable for limited grades of SC bimetallic steel. This paper aims to develop a simplified constitutive model applicable to various SC bimetallic steels with different clad-substrate combinations and clad ratios. To this end, the expression of two-stage stress-strain model proposed by Mirambell and Real is selected due to its popularity and recognition. The breakpoint of the two evolutionary stage is determined as the yield plateau termination point of the corresponding substrate metal. Through a thorough analysis on 156 thousands simulated stress-strain curves, the key description parameters of such stress-strain expression, including the strength and strain corresponding to the breakpoint and ultimate point, the tangent modulus and strain hardening components corresponding to two evolutionary stages, were correlated with the influencing factors including the clad ratio, strain and strength indexes of clad and substrate metals. Subsequently, the fitting performances of the proposed constitutive models were validated through existing experimental curves and numerical simulation curves. Accordingly, the different definitions of yield strength and ultimate strength of SC bimetallic steel were compared and discussed.

Insight into ideal shear strength of Ni-based dilute alloys using first-principles calculations and correlational analysis

The present work examines the effect of alloying elements (denoted X) on the ideal shear strength for 26 dilute Ni-based alloys, Ni11X, as determined by first-principles calculations of pure alias shear deformations. The variations in ideal shear strength are quantitatively explored with correlational analysis techniques, showing the importance of atomic properties such as size and electronegativity. The shear moduli of the alloys are affirmed to show a strong linear relationship with their ideal shear strengths, while the shear moduli of the individual alloying elements were not indicative of alloy shear strength. Through combination with available ideal shear strength data on Mg alloys, a potential application of the Ni alloy data is demonstrated in the search for a set of atomic features suitable for machine learning applications to mechanical properties. As another illustration, the calculated Ni ideal shear strengths play a key role in a predictive multiscale framework for deformation behavior of single crystal alloys at large strains, as shown by simulated stress–strain curves.

Prediction of Fracture Toughness Scatter Based on Weibull Stress Using Crystal Plasticity Finite Element Method

A multi-scale prediction method was proposed to investigate the scatter of fracture toughness by combining the local approach (LA) to cleavage fracture and the crystal plasticity finite element method (CPFEM). The parameters in the crystal plasticity constitutive model were firstly determined by comparing the simulated stress-strain curves with tested curves for SA508-III steel. Then CT samples were modeled using the CPFEM to calculate Weibull stress. Using the calibration process of local approach, the relevant parameters of the Beremin model were obtained with m = 30 and σu = 2590 MPa. The fracture toughness was analyzed including the scatter for a given temperature, the master curve in a temperature range. The distribution of predicted fracture toughness shows good agreement with the test results. All of the tested fracture toughness value are fall in the range of 5% to 95% that precited using the proposed combined approach.

Fracture in Silica/Butadiene Rubber: A Molecular Dynamics View of Design-Property Relationships.

Despite intense investigation, the mechanisms governing the mechanical reinforcement of polymers by dispersed nanoparticles have only been partially clarified. This is especially true for the ultimate properties of the nanocomposites, which depend on their resistance to fracture at large deformations. In this work, we adopt molecular dynamics simulations to investigate the mechanical properties of silica/polybutadiene rubber, using a quasi-atomistic model that allows a meaningful description of bond breaking and fracture over relatively large length scales. The behavior of large nanocomposite models is explored systematically by tuning the cross-linking, grafting densities, and nanoparticle concentration. The simulated stress-strain curves are interpreted by monitoring the breaking of chemical bonds and the formation of voids, up to complete rupture of the systems. We find that some chemical bonds, and particularly the S-S linkages at the rubber-nanoparticle interface, start breaking well before the appearance of macroscopic features of fracture and yield.

Visualization of the damage evolution for Ti–3Al–2Mo–2Zr alloy during a uniaxial tensile process using a microvoids proliferation damage model

Abstract Understanding the damage evolution of alloys during a plastic deformation process is significant to the structural design of components and accident prevention. In order to visualize the damage evolution in the plastic deformation of Ti–3Al–2Mo–2Zr alloy, a series of uniaxial tensile experiments for this alloy were carried out under the strain rates of 0.1–10 s−1 at room temperature, and the stress–strain curves were achieved. On the other hand, the finite element (FE) models of these uniaxial tensile processes were established. A microvoids proliferation model, Gurson–Tvergaard–Needleman (GTN) damage model, was implanted into the uniaxial tensile models, and the simulated stress–strain curves corresponding to different GTN parameter combinations were obtained. Based on the simulated and experimental stress–strain curves, the GTN parameters of this alloy were solved by response surface methodology (RSM). The solved GTN parameters suggest that higher strain rate can enhance the proliferation and coalescence of microvoids. Furthermore, the uniaxial tensile tests over different strain rates were simulated using the solved GTN parameters. Then, the damage processes were visualized and evaluated. The result shows that the degradation speed of this alloy is slow at the initial stage of the tensile deformation and then accelerates once the voids volume fraction reaches a critical value.