Dependence Of Strength Research Articles

Experimental Investigation and Micromechanics-Based Analytical Modeling of Creep and Relaxation Behaviors of Beishan Granite

This paper investigates experimentally and numerically the short- and long-term strength and deformation behaviors of Beishan granite at room temperature. Single-stage creep, relaxation, and conventional triaxial compression tests were performed on cylindrical rock samples. Its typical brittle response is captured and the dependence of peak strength on confining pressure and time-dependent response on deviatoric stress are revealed. For constitutive modeling, a unified micromechanics-based plasticity-damage model is formulated based on the Mori–Tanaka method and the subcritical cracking theory postulate, with the focus on simulating both instantaneous strain and time-dependent deformation process over a broad range of time scales. Its unification is achieved by representing the evolution of damage, which is strongly coupled with plastic deformation induced by frictional sliding along closed cracks, as an internal variable that can be decomposed into instantaneous and time-dependent parts. The performance of the model with analytical predictions is well validated using the experimental results on Beishan granite.

Effective stress analysis of dynamically installed anchor installation in rate-dependent clay

Accurate prediction of the final embedment depth and installation-induced excess pore pressure of dynamically installed anchors (DIAs) are prerequisites for the design of subsequent anchor set-up during a waiting period and capacity under operational loadings. This paper presents a dynamic large deformation finite element approach within the effective stress framework and investigates the installation behaviour of DIAs in clay. An elasto-viscoplastic model is adopted to capture strain rate dependency of the undrained shear strength. Development of excess pore pressure for various impact velocities, anchor geometries, viscosity parameters are quantified. An expression is proposed for estimating the final embedment depth of DIAs in clay.

Microstructure design and mechanical properties of grain-gradient graphene/aluminum composites

The metal matrix with mixed grain-gradient structure and the graphene with different characteristics could be designed and prepared to ameliorate the plasticity and toughness reduction of the metal matrix composites (MMCs) caused by graphene reinforcement. However, the relationship between the microstructure and the mechanical properties of composites needs to be investigated. In this paper, a self-developed structural modeling program is employed to design and establish a single-edge notch tensile finite element model of the graphene reinforced grain-gradient aluminum (Al) matrix composites, where the distribution and morphology of graphene and grains can be redistributed. Then, the grain size dependence of yield strength is introduced into the developed crystal plasticity finite element method (CPFEM) according to the classical Hall-Petch relationship, the damage mechanism of the graphene/Al composites with various designed novel microstructures is analyzed in combination with the cohesive zone model (CZM), and the microstructure of the graphene/Al composites with optimal mechanical properties is obtained. In addition, it is found that the failure mode, strength and toughness of the composites could be ameliorated by adjusting the bonding state of graphene-Al interface. This study provides a new insight into the microstructure design and fabrication of the graphene/Al composites with optimal comprehensive properties.

Real-space, real-time approach to quantum-electrodynamical time-dependent density functional theory.

The quantum-electrodynamical time-dependent density functional theory equations are solved by time propagating the wave function on a tensor product of a Fock-space and real-space grid. Applications for molecules in cavities show the accuracy of the approach. Examples include the coupling strength and light frequency dependence of the energies, wave functions, optical absorption spectra, and Rabi splitting magnitudes in cavities, as well as a description of high harmonic generation in cavities.

Spin-Enhanced C–C Coupling in CO 2 Electroreduction with Oxide-Derived Copper

Spin-Enhanced C–C Coupling in CO ₂ Electroreduction with Oxide-Derived Copper

Chemical-substitution dependence of magnetization strength in room- temperature ferromagnetism of dilute magnetic oxides: Valence and spin state of slightly doped cobalt in (In,Al)2O3

This study investigates the valence and spin states of cobalt ions and the magnitude of room-temperature ferromagnetic magnetization in In1.9−xAlxCo0.1O3 (0≤x≤0.3) prepared by a chemical solution method. According to X-ray photoelectron spectroscopy, the Co ions in the Al-free sample (x=0) existed in a mixed state of trivalent Co3+ and divalent Co2+. The abundance ratio of Co2+ increased with Al content, and only divalent ions were present at x=0.3. A magnetic susceptibility analysis showed that both the spin and orbital degrees of freedom were magnetized in Co2+, whereas Co3+ was in a low-spin state. Co3+ was converted to Co2+ by vacuum annealing. The higher the conversion ratio of Co3+ to Co2+, the stronger was the room-temperature ferromagnetism.

Structural optimization of lattice cellular structures: incorporating the fatigue strength dependency on the building orientation of sub-unit struts

Structural optimization of lattice cellular structures: incorporating the fatigue strength dependency on the building orientation of sub-unit struts

FORMABILITY OF INVAR 36 ALLOY AT HIGH TEMPERATURES

By using of hot tensile tests, which were performed on simulator HDS-20, the formability of Invar 36 alloy was investigated. By a special type of a tensile test, involving a continuous control heating of the tested specimens and their simultaneous load by a constant tensile force of 80 N, a nil-strength temperature of investigated alloy 1419 °C was determined. By continuous uniaxial tensile tests to rupture the strength and plastic properties of the Invar 36 alloy were determined in the wide range of deformation temperatures (from 800 °C to 1390 °C) and mean strain rates (from 0.09 s-1 to 75 s-1). On the basis of obtained results the 3D maps were constructed, expressing the dependence of the contractual hot ultimate tensile strength, hot ductility and hot reduction of area of the Invar 36 alloy on the deformation temperature and on the mean strain rate. Based on the determined plastic properties, the nil-ductility temperature of the investigated alloy of 1390 °C was also determined.

Modeling transient resonances in extreme-mass-ratio inspirals

Extreme-mass-ratio inspirals are one of the most exciting and promising target sources for space-based interferometers (such as LISA, TianQin). The observation of their emitted gravitational waves will offer stringent tests on general theory of relativity, and provide a wealth of information about the dense environment in galactic centers. To unlock such potential, it is necessary to correctly characterize EMRI signals. However, resonances are a phenomena that occurs in EMRI systems and can impact parameter inference, and therefore the science outcome, if not properly modeled. Here, we explore how to model resonances and develop an efficient implementation. Our previous work has demonstrated that tidal resonances induced by the tidal field of a nearby astrophysical object alters the orbital evolution, leading to a significant dephasing across observable parameter space. Here, we extensively explore a more generic model for the tidal perturber with additional resonance combinations, to study the dependence of resonance strength on the intrinsic orbital and tidal parameters. To analyze the resonant signals, accurate templates that correctly incorporate the effects of the tidal field are required. The evolution through resonances is obtained using a step function, whose amplitude is calculated using an analytic interpolation of the resonance jumps. We benchmark this procedure by comparing our approximate method to a numerical evolution. We find that there is no significant error caused by this simplified prescription, as far as the astronomically reasonable range in the parameter space is concerned. Further, we use Fisher matrices to study both the measurement precision of parameters and the systematic bias due to inaccurate modeling. Modeling of self-force resonances can also be carried out using the implementation presented in this study, which will be crucial for EMRI waveform modeling.

Strong band renormalization and emergent ferromagnetism induced by electron-antiferromagnetic-magnon coupling

The interactions between electrons and antiferromagnetic magnons (AFMMs) are important for a large class of correlated materials. For example, they are the most plausible pairing glues in high-temperature superconductors, such as cuprates and iron-based superconductors. However, unlike electron-phonon interactions (EPIs), clear-cut observations regarding how electron-AFMM interactions (EAIs) affect the band structure are still lacking. Consequently, critical information on the EAIs, such as its strength and doping dependence, remains elusive. Here we directly observe that EAIs induce a kink structure in the band dispersion of Ba1−xKxMn2As2, and subsequently unveil several key characteristics of EAIs. We found that the coupling constant of EAIs can be as large as 5.4, and it shows strong doping dependence and temperature dependence, all in stark contrast to the behaviors of EPIs. The colossal renormalization of electron bands by EAIs enhances the density of states at Fermi energy, which is likely driving the emergent ferromagnetic state in Ba1−xKxMn2As2 through a Stoner-like mechanism with mixed itinerant-local character. Our results expand the current knowledge of EAIs, which may facilitate the further understanding of many correlated materials where EAIs play a critical role.

Testing and modeling clay behavior subjected to high strain rate loading in a tunneling problem

Complex numerical simulations of tunnels are often used to model effects of high strain rate surface loads. Most of this modeling ignores soil's strength dependency on strain rate to lessen the complexity. A series of Split Hopkinson Pressure Bar (SHPB) tests emulates the high strain rate compression occurring in blast events, for Nile Silty Clay (NSC) samples. The Cowper Symonds parameters are calibrated to SHPB test results and are used in advanced three-dimensional finite element analysis of a benchmark tunnel problem using Abaqus/Explicit software. The shallow tunnel in NSC formation is subjected to a blast event at the ground surface simulated by the CONWEP algorithm. The Smoothed Particle Hydrodynamic (SPH) mesh-free technique captures the crater formed due to the explosion. Results from the benchmark problem show that including the strain rate dependency in the analysis leads to a significant reduction in the calculated tunnel liner straining actions and deformations.

Critical review of the Mogi failure criterion based on true-triaxial laboratory data analysis and theoretical considerations

The influence of the intermediate principal stress , σ 2 , is disregarded when rock strength is analyzed using the Mohr-Coulomb or Hoek-Brown criteria. Several polyaxial strength criteria have been proposed to account for the influence of σ 2 . One of the methods that received considerable attention is the Mogi criterion. The criterion modifies the Nadai or Drucker-Prager approaches by exchanging the normal octahedral stress with what is introduced as the mean effective stress, σ m ,2 . This change is based on experimental evidence that the influence of the intermediate principal stress on strength is less pronounced than the influence of the minimum principal stress. However, the Mogi criterion was derived somewhat empirically and consequently it is essential to analyze its potential theoretical deficiencies. In the current note, we analyzed the Mogi failure criterion, describing its characteristics in both τ oct – σ m ,2 and σ 1 - σ 2 spaces. We investigated the relation between Mohr-Coulomb and Mogi criteria, which marks the basis for the commonly used Mogi-Coulomb approach. We compared the performance of the Mogi criterion against available polyaxial strength data using three fitting approaches: Mogi-Coulomb based on triaxial compression results only, linear Mogi based on all polyaxial strength results, and power law Mogi also based on all data. The analysis reveals several serious deficiencies of the Mogi approach which all suggest that the Mogi criterion cannot properly represent the σ 2 dependence of rock strength in many cases.

Effect of layer height, infill geometry, nozzle temperature, and fan speed on tensile strength of 3D printing PETG specimens

This research is aimed to provide insight on the dependency of tensile strength on process parameters of the Fused Deposition Modeling (FDM). FDM is one of the most popular 3D printing manufacturing techniques. In the present study, a tensile test was performed to measure the tensile strength of PETG (Polyethylene terephthalate glycol) specimen with the combination of different layer height, infill geometry, nozzle temperature, and fan speed whereas other parameters are kept at a constant level. This study uses the ISO 527 1BA standard. Taguchi L16 (44) with 4 levels for each factor was used to determine the effect of each parameter. Each experiment repeated 3 times to minimize the occurrence of errors. layer height, infill geometry, nozzle temperature, and fan speed ​​respectively effect of 13.4%, 63.6%, 19.0%, and 2.7%. Fan speed is considered a parameter that has no impact on tensile strength. The layer height and nozzle temperature parameter shows that the higher the value, the tensile strength of specimens tend to increase. Furthermore, infill geometry from the one with the highest to the lowest tensile strength value is gyroid, zig-zag, grid, and triangles. The combination of layer height of 0.24 mm, infill geometry gyroid, and nozzle temperature of 250 ˚C is the optimum combination of parameters which has the highest tensile strength of 34.76 N/mm2.

Evaluation of copper spall response using Mie-Grüneisen equation-of-state parameters determined from molecular dynamics

In this study, the formation and application of an across-scale modeling approach is presented to study the influence of shock loading conditions on copper spallation performance. Molecular dynamics simulations coupled with multi-scale shock technology are conducted to determine characteristic parameters of the Mie-Grüneisen equation of state involved in the Slater and Dugdale-MacDonald models. Afterwards, the resultant parameters are embedded into the finite element method to explore the dependence of spall strength, strain rate, and damage evolution rate. It is found that an increase in loading velocity promotes the spallation occur in advance. Combined with free surface velocity and spall plane pressure, it is also discovered that the material experiences an entire spallation prior to ''pullback signal''. As expected, the spall strength determined as the maximum stress is higher than that estimated from the free surface velocity. Besides, there is a temperature-rise effect caused by void-induced thermal dissipation during the spallation. Moreover, the position of spall plane is strongly dependent upon flyer thickness, thereby exhibiting a strain rate effect on spallation behavior. A comparison between numerical results and published experimental data highlights the adequacy of such a hybrid method to capture the copper spall response.

Experimental study of dynamic biaxial compressive properties of full grade aggregate concrete after freeze thaw cycles

Most hydraulic concrete structures are in complex stress state, this study attempts to take some test of full grade aggregate concrete under biaxial compression after 0, 25, 50, 75, and 100 cycles of freeze-thaw. Five principle compression stress ratios of 1:0, 1:0.25, 1:0.5, 1:0.75 and 1:1 and four different strain rates of 10−5/s, 10−4/s, 10−3/s and 10−2/s were the main variables. The mass loss of concrete after freeze-thaw cycles has been studied. With the increase of freeze-thaw cycles, the quality loss is little. The failure pattern, ultimate strength, peak strain and stress-strain curve under different freeze-thaw cycles, stress ratios and strain rates were obtained. The dependence of ultimate strength on freeze-thaw cycles and ultimate strength, and the relationship between freeze-thaw cycles, stress ratio and strain rate were analyzed according to the testing data. The unified failure criterion of full grade aggregate concrete after freeze-thaw cycles under dynamic biaxial compressive stress state was established in principal stress space and octahedral stress space, respectively. The comparative analysis of experimental results of different types of concrete(large aggregate concrete, ordinary concrete, lightweight aggregate concrete, wet screened concrete) under biaxial compression after freeze-thaw cycles are made. With the increase of freeze-thaw cycles, the ultimate compressive strength of common concrete, wet screened concrete, lightweight aggregate concrete and large aggregate concrete gradually decreases. The results may serve as an experimental and theoretical reference for the design and maintenance of hydraulic structures.

Stable binding to phosphatidylserine-containing membranes requires conserved arginine residues in tandem C domains of blood coagulation factor VIII.

At sites of vascular damage, factor VIII (fVIII) is proteolytically activated by thrombin and binds to activated platelet surfaces with activated factor IX (fIXa) to form the intrinsic "tenase" complex. Previous structural and mutational studies of fVIII have identified the C1 and C2 domains in binding to negatively charged membrane surfaces through β-hairpin loops with solvent-exposed hydrophobic residues and a ring of positively charged basic residues. Several hemophilia A-associated mutations within the C domains are suggested to disrupt lipid binding, preventing formation of the intrinsic tenase complex. In this study, we devised a novel platform for generating recombinant C1, C2, and C1C2 domain constructs and performed mutagenesis of several charged residues proximal to the putative membrane binding region of each C domain. Binding measurements between phosphatidylserine (PS)-containing lipid membrane surfaces and fVIII C domains demonstrated an ionic strength dependence on membrane binding affinity. Mutations to basic residues adjacent to the surface-exposed hydrophobic regions of C1 and C2 differentially disrupted membrane binding, with abrogation of binding occurring for mutations to conserved arginine residues in the C1 (R2163) and C2 (R2320) domains. Lastly, we determined the X-ray crystal structure of the porcine fVIII C2 domain bound to o-phospho-L-serine, the polar headgroup of PS, which binds to a basic cleft and makes charge-charge contact with R2320. We conclude that basic clefts in the fVIII C domains bind to PS-containing membranes through conserved arginine residues via a C domain modularity, where each C domain possesses modest electrostatic-dependent affinity and tandem C domains are required for high affinity binding.

The Dependence of the Strength of a Carbon Fiber/Aluminum Matrix Composite on the Interface Shear Strength between the Matrix and Fiber

Taking the example of a composite wire with an Al-25% Sn alloy matrix reinforced with carbon fiber, the dependence of composite bending strength on interface shear strength was determined. Samples of the composite wire with different interface shear strengths were obtained by heat treatment at temperatures from 300 to 600 °C. The highest bending strength of 2450 MPa was observed for composite wire samples with the lowest interface shear strength. With an increase in the shear strength of the interface, a decrease in the strength was observed. The study of the surface of carbon fiber extracted from the composite showed that heat treatment led to the formation of aluminum carbide crystals on the fiber surface, the size and number of which increased with increasing temperature. As a result, there was an increase in the shear strength of the interface. The evaluation of the work of fracture of a composite with different strengths of the interface between the matrix and the fiber demonstrated that as the strength of the interface increases, the work of fracture decreases, due to the premature fracture of the composite through crack propagation in one plane. Based on the experimental data, the refined mixture rule according to the Weibull distribution, and an assessment of the critical stress of crack propagation according to the Griffith–Orowan–Irwin concept, the dependence of composite strength on the shear strength of the interface was estimated. Due to this, the critical shear strength was calculated at which the greatest strength of the composite can be achieved, these values being 107 MPa and 2675 MPa, respectively. It is shown that the contribution of the work of overcoming the friction force to the total work of fracture at relatively small values of shear strength can be several times greater than the total contribution of all other types of energy.

Mechanical characteristics and failure morphology of FFF-printed poly lactic acid composites reinforced with carbon fibre, graphene and MWCNTs

Fused Filament Fabrication (FFF) is the most prevalent additive manufacturing technique, which involves extruding a softened thermoplastic filament through the nozzle of a heated extruder. For improving the mechanical properties of the FFF-printed PLA parts one of the options is to add reinforcing material, such as carbonaceous materials or metal particles. The present study deals with analysing and comparing mechanical properties of carbon fibre reinforced poly lactic acid (CF-PLA), graphene reinforced PLA (Gr-PLA) and multi walled carbon nano tubes reinforced PLA (MWCNTs-PLA) composites by FFF. The selected process parameters used in this study are raster angle (0°, 45°, 90°), feed rate (20 mm/s, 40 mm/s, 60 mm/s) and layer height (0.1 mm, 0.15 mm, 0.2 mm) and based on different combinations, elongation at break, modulus and tensile strength are examined. MWCNTs-PLA exhibits overall maximum tensile strength, 37.438 MPa with 15.384% elongation at break for layer height 0.1 mm, raster angle 0° and feed rate 20 mm/s as compared to other selected specimens. Fractography analysis is also done to better understand the failure modes of specimens. To examine the dependency of the tensile strength on the process parameters, ANOVA, Taguchi’s L9 array Design of Experiment (DOE) is utilized indicating that layer height has the highest contribution of 56.713% for Gr-PLA, but raster angle has the highest contribution of 54.899% and 76.16% for CF-PLA and MWCNTs-PLA, respectively. This work will help in better understanding of how different parameters effects the material properties for PLA composites.

Metallographic Study of Overlapped Laser Welds of Dissimilar Materials

The paper deals with the metallographic analysis of overlapped laser welds of dissimilar materials based on galvanized and ungalvanized steels in various combinations. In addition to a gallery of metallographic sections, the paper presents the monitoring of weld defects, the measurement of selected weld geometrical characteristics and changes in weld microstructure by measuring the microhardness profile across the joint. The mixing of materials was monitored by area and line EDX analysis in the melting zone. Subsequently, the load carrying capacity of the formed joints was determined and compared with FEM simulation. Finally, the dependences of hardness and strength of welds on carbon content and carbon equivalent were determined.

An Improved Particle Impact Model by Accounting for Rate of Strain and Stochastic Rebound

Abstract A methodology for informing physics-based impact and deposition models through the use of novel experimental and analysis techniques is presented. Coefficient of restitution (CoR) data were obtained for Arizona Road Dust (ARD), AFRL02 dust, and each component of AFRL02 impacting a Hastelloy X plate at a variety of flow temperatures (295–866 K), surface temperatures (295–1255 K), particle velocities (0–100 m/s), and impact angles (0–90 deg). High speed particle shadow velocimetry (PSV) allowed individual impact data to be obtained for more than 8 million particles overall, corresponding to 20 combinations of particle composition, flow temperature, and surface temperature. The experimental data were applied to an existing physics-based particle impact model to assess its ability to accurately capture the physics of particle impact dynamics. Using the experimental data and model predictions, two improvements to the model were proposed. The first defined a velocity-dependent “effective yield strength,” designed to account for the effects of strain hardening and strain rate during impact. The second introduces statistical spread to the model output, accounting for the effect of randomizing variables such as particle shape and rotation. Both improvements were demonstrated to improve the model predictions significantly. Applying the improved model to the experimental data sets, along with known temperature-dependent material properties such as the elastic modulus and particle density, allowed the temperature dependence of the effective yield strength to be determined. It was found that the effective yield strength is not a function of temperature over the range studied, suggesting that changes in other properties are responsible for differences in rebound behavior. The improved model was incorporated into a computational simulation of an impinging flow to assess the effect of the model improvements on deposition predictions, with the improved model obtaining deposition trends that more closely match what has been observed in previous experiments. The work performed serves as a stepping stone towards further improvement of physics-based impact and deposition models through refinement of other modeled physical processes.