Uniaxial Tensile Mechanical Properties Research Articles

Mechanical properties and flow stress constitutive relationship of Ti–6Al–4V alloy with equiaxed microstructure at cryogenic temperatures

This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to 298 K and strain rates from 10−4/s to 10−2/s. Scanning electron microscopy is utilized to analyze the fracture morphology, aiming to reveal the fracture behavior at various temperatures. The applicability of the Zener-Hollomon parameter and the Johnson-Cook model in describing the flow stress of Ti-6Al-4V at cryogenic temperatures is analyzed. Moreover, a constitutive relationship modeling method based on the variational recurrent networks is proposed. Mechanical test results show a significant increase in the strength of equiaxed Ti-6Al-4V alloy under cryogenic conditions while the plastic deformation process is shortened. However, the fracture analysis indicates that even at 77 K, the fracture process is still dominated by ductile fracture, and brittle fracture does not occur within the range of 77 K to 298 K. The fitting results validate the performance of the Zener-Hollomon parameter and the Johnson-Cook model in describing the deformation flow stress of Ti-6Al-4V alloy at cryogenic temperatures. The results also indicate that the proposed constitutive relationship modeling method based on the variational recurrent network performs better, making it a potential method for widespread applications.

Interatomic potential of the MgAl2O4/Al interface and its application in strengthening mechanisms

MgAl2O4 ceramics possess outstanding mechanical properties, making them promising for use as reinforcing or interfacial modulating phase in Al-based metal composites. The challenge lies in the insufficient interatomic potential parameters to accurately characterize the MgAl2O4/Al interfacial interactions, which hampers a detailed understanding of the interfacial strengthening mechanisms at the atomic level. Since the pair potential satisfies the requirements for computational efficiency and accuracy, it has been widely used for investigating the interfacial properties of composite materials. In this study, the interatomic potential parameters for Al–Mg and Al–Al bonds were derived from Buckingham potential, while those for Al–O bonds were obtained from Morse potential via first principles calculations. The uniaxial tensile mechanical properties and interface-dislocation strengthening mechanisms of MgAl2O4/Al interface configuration were explored through molecular dynamics simulations. The analyses reveal that the strength enhancement of the MgAl2O4/Al interface is due to the generation of a large number of immovable 1/6<110> stair-rod dislocations therein. The thickness of MgAl2O4 layer significantly influences the mechanical properties. Below a thickness of 20 Å, the presence of movable dislocations reduces the strengthening effect. Conversely, increasing the thickness of MgAl2O4 encourages the emergence of immovable dislocations and increases the flow stress, while the corresponding yield strain decreases. These insights open up new prospects in the development of aluminum metal matrix composites with enhanced performance.

Analysis of fracture damage mechanical properties of particle reinforced polymer composite film based on micro-macro finite element method

The particle reinforcement and related effect on fracture damage mechanical properties of polymers have been studied in this paper. Based on the uniaxial tensile test result of SiO2 particle reinforced polyvinylidene fluoride (PVDF) composites, the parameters of macro elastic-plastic finite element model and micro particle reinforced model are obtained. The effects of boundary conditions, shape and size of damage notch on fracture damage mechanical properties of PVDF composites are studied from macroscopic view. The uniaxial tensile mechanical properties and elastic modulus are increased with notch angle (0°, 30°, 60°, 120°). The damage analysis of the micro model shows that the mechanical properties of SiO2/PVDF composites are best when the content of SiO2 is 6%. Debonding between particles and matrix indicates have great effect on crack propagation. The micro-macro finite element model is effective tool to study the damage mechanical properties of particle reinforced polymers.

Effect of gradient nanostructures on the damage mechanism of aermet100 steel at various strain rates

The introduction of nano-scale grains, which form a gradient nanostructure (GNS) within the material, usually increases the service life of metallic materials. In this study, the uniaxial tensile mechanical properties of AerMet100 steel in initial and GNS states under different strain rate conditions were compared, and the microanalysis of tensile fracture was performed. It is found that GNS has little effect on the mechanical properties of AerMet100 but has an effect on its damage mode. The initial AerMet100 was basically ductile fracture, and GNS increased the brittle fracture mode in AerMet100.

Tensile properties of transversely isotropic closed-cell PVC foam under quasi-static and dynamic loadings

The uniaxial tensile mechanical properties of PVC foam considering the effects of strain rate ([Formula: see text]) and anisotropy ([Formula: see text]) have been investigated by quasi-static and dynamic (Split Hopkinson Tensile Bar, SHTB) tests. Combined high-speed camera system and Digital Image Correlation (DIC) technique, the real-time surface strain field of the specimen during the whole tensile process was obtained. On this basis, the macroscopic response and failure mode of PVC foam were investigated. The failure mechanism of PVC foam under tensile loading was revealed through Scanning Electron Microscope (SEM) images on fracture cross-section of loaded specimen. Finally, based on experimental data, a prediction equation on tensile strength of PVC foam considering the effects of strain rate and loading angle (anisotropy) is proposed. Furthermore, a nonlinear constitutive model is developed to describe the uniaxial tensile mechanical properties of PVC foam.

Non-enzymatic glycation increases the failure risk of annulus fibrosus by predisposing the extrafibrillar matrix to greater stresses.

Growing clinical evidence suggests a correlation between diabetes and more frequent and severe intervertebral disc failure, partially attributed to accelerated advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF) through non-enzymatic glycation. However, in vitro glycation (i.e., crosslinking) reportedly improved AF uniaxial tensile mechanical properties, contradicting clinical observations. Thus, this study used a combined experimental-computational approach to evaluate the effect of AGEs on anisotropic AF tensile mechanics, applying the finite element models (FEM) to complement experimental testing and examine difficult-to-measure subtissue-level mechanics. Methylglyoxal-based treatments were applied to induce three physiologically relevant AGE levels in vitro. Models incorporated crosslinks by adapting our previously validated structure-based FEM framework. Experimental results showed that a threefold increase in AGE content resulted in a ∼55% increase in AF circumferential-radial tensile modulus and failure stress and a 40% increase in radial failure stress. Failure strain was unaffected by non-enzymatic glycation. Adapted FEMs accurately predicted experimental AF mechanics with glycation. Model predictions showed that glycation increased stresses in the extrafibrillar matrix under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling, providing insight into the relationship between AGE accumulation and increased tissue failure. Our findings also added to the existing literature regarding crosslinking structures, indicating that AGEs had a greater effect along the fiber direction, while interlamellar radial crosslinks were improbable in the AF. In summary, the combined approach presented a powerful tool for examining multiscale structure-function relationships with disease progression in fiber-reinforced soft tissues, which is essential for developing effective therapeutic measures. STATEMENT OF SIGNIFICANCE: : Increasing clinical evidence correlates diabetes with premature intervertebral disc failure, likely due to advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF). However, in vitro glycation reportedly increases AF tensile stiffness and toughness, contradicting clinical observations. Using a combined experimental-computational approach, our work shows that increases in AF bulk tensile mechanical properties with glycation are achieved at the risk of exposing the extrafibrillar matrix to increased stresses under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling. Computational results indicate that crosslinks along the fiber direction account for 90% of the increased tissue stiffness with glycation, adding to the existing literature. These findings provide insight into the multiscale structure-function relationship between AGE accumulation and tissue failure.

Static Stiffness Properties of High Load Capacity Non-Pneumatic Tires with Different Tread Structures

A high load capacity non-pneumatic tire (HC tire) was designed and manufactured to solve the problems of air leakage, puncture, blowout, shoulder void, and delamination, which occur in traditional high load capacity tires, as well as significantly increase the unit load of tires. Experiments and numerical simulations were conducted to investigate the static stiffness properties of the HC tire. Additionally, the manufacturing process of the tire was highlighted. The tire mainly comprised polyurethane and silicon manganese steel, and a ‘π’-shaped support substructure was adopted. The tread structure was made up of a built-in spiral steel ring and a non-steel ring. The uniaxial tensile mechanical properties of the used metal and elastomer materials were tested, and the linear elastic constitutive model and Marlow constitutive model, respectively, were used to describe their mechanical characteristics. The stiffness properties of the HC tire, including torsional, longitudinal, vertical, and lateral stiffnesses, were evaluated using a tire comprehensive stiffness tester. Nonlinear finite element models of the HC tire were established, and their accuracies were verified through vertical stiffness tests. The stiffness properties of the HC tire in other directions were simulated as well. An in-depth comparative analysis of the simulation and experimental data was performed. The results demonstrated that the unit load of the unreinforced HC tire was 2.972 times and 1.615 times higher than that of the solid tire and pneumatic tire, respectively. The spiral steel ring embedded in the tread increased the vertical and longitudinal stiffness but reduced the torsional stiffness of the HC tire, thus reversing the variation trend of the lateral stiffness at the 0° and 5° test points. The findings can serve as a reference for theoretical research on, and the structural optimization of, non-pneumatic tires with a high load capacity.

Temperature- and Defect-Induced Uniaxial Tensile Mechanical Behaviors and the Fracture Mechanism of Two-Dimensional Silicon Germanide.

Recently, monolayer silicon germanide (SiGe), a newly explored buckled honeycomb configuration of silicon and germanium, is predicted to be a promising nanomaterial for next-generation nanoelectromechanical systems (NEMS) due to its intriguing electronic, optical, and piezoelectric properties. In the NEMS applications, the structure is subjected to uniaxial tensile mechanical loading, and the investigation of the mechanical behaviors is of fundamental importance to ensure structural stability. Here, we systematically explored the uniaxial tensile mechanical properties of 2D-SiGe through molecular dynamics simulations. The effects of temperature ranges from 300 to 1000 K and vacancy defects, for instance, point and bi vacancy, for both armchair and zigzag orientations of 2D-SiGe were investigated. In addition, the influence of system areas and strain rates on the stress–strain performance of 2D-SiGe has also been studied. With the increase in temperature and vacancy concentration, the mechanical properties of 2D-SiGe show decreasing behavior for both orientations and the armchair chirality shows superior mechanical strength to the zigzag direction due to its bonding characteristics. A phase transformation-induced second linearly elastic region was observed at large deformation strain, leading to an anomalous stress–strain behavior in the zigzag direction. At 300 K temperature, we obtained a fracture stress of ∼94.83 GPa and an elastic modulus of ∼388.7 GPa along the armchair direction, which are about ∼3.17 and ∼2.83% higher than the zigzag-oriented fracture strength and elastic modulus. Moreover, because of the strong regularity interruption effect, the point vacancy shows the largest decrease in fracture strength, elastic modulus, and fracture strain compared to the bi vacancy defects for both armchair and zigzag orientations. Area and strain rate investigations reveal that 2D-SiGe is less susceptible to the system area and strain rate. These findings provide a deep insight into controlling the tensile mechanical behavior of 2D-SiGe for its applications in next-generation NEMS and nanodevices.

Test of Uniaxial Tensile Mechanical Properties of ECTFE Foils at Various Temperatures

Test of Uniaxial Tensile Mechanical Properties of ECTFE Foils at Various Temperatures

Two-dimensional graded metamaterials with auxetic rectangular perforations

This work describes the in-plane uniaxial tensile mechanical properties of two-dimensional graded rectangular perforations metamaterials using numerical homogenization finite element approaches benchmarked by experimental results. The metamaterial configuration is based on graded patterns of centre-symmetric perforated cells that can exhibit an auxetic (negative Poisson’s ratio) behavior. Global and local equivalent mechanical properties of the metamaterial are measured using digital image correlation techniques mapped over Finite Element models to identify strain patterns and related stress distributions at different scales. The samples and their numerical counterpart are parametrized against the spacing and aspect ratios of the cells. The overall stiffness behavior of the graded perforated metamaterial plates features a higher degree of compliance that depends both on the geometries of the cells of the graded areas, but also on the graded pattern used. Local Poisson’s ratio effects show a general constraint of the auxetic behavior compared to the case of uniform plates, but also interesting and controllable shape changes due to the uniaxial tensile loading applied.

Experimental Investigation and Constitutive Description of Railway Wheel/Rail Steels under Medium-Strain-Rate Tensile Loading

The uniaxial tensile mechanical properties of D1 wheel steel and U71MnG rail steel were investigated experimentally at a wide range of strain rates from 0.0001 to 100 s−1. Influence of the strain rate on stress–strain response, ductility, fracture morphology and energy absorption was analyzed and discussed, respectively. Both D1 wheel steel and U71MnG rail steel are demonstrated to be strain rate sensitive, and D1 wheel steel specimens generally exhibit a larger elongation and a better ductility than U71MnG rail steel specimens at each strain rate. The fracture mechanism of D1 wheel steel is a ductile fracture at lower strain rates and quasi-ductile fracture at higher strain rates, while U71MnG rail steel tends to a quasi-ductile fracture at lower strain rates and a brittle fracture at higher strain rates. The specific energy absorption values of D1 wheel steel and U71MnG rail steel increase with the increase in true strain and elevated strain rate. Finally, the Johnson–Cook model is adopted to predict the stress–strain response of wheel/rail steels studied, and a better agreement is found.

Uniaxial Tensile Properties of Atherosclerotic Carotid Artery After Mobilization of Pushing on Qiao-Gong: A Safety Study Using an Animal Model of Carotid Atherosclerosis

ObjectivesThis study aimed to preliminarily explore the effects of the soft tissue mobilization of pushing on Qiao-Gong (MPQ) on biomechanical properties of the carotid artery using an animal model of carotid atherosclerosis (CAS). MethodsFifty rabbits were randomly divided into 4 groups: animals with CAS treated with MPQ (CAS-MPQ [n = 15]); animals with CAS treated without MPQ (CAS [n = 15]); normal animals treated with MPQ (normal-MPQ [n = 10]); and a blank control group (n = 10). The MPQ procedure consisted of soft tissue mobilization of the Qiao-Gong acupoint on the front edge of the sternocleidomastoid muscle applied from top to bottom, by flat pushing with the thumb repeatedly for 20 times. Disease in the CAS models was induced by carotid artery balloon injury combined with a high-fat diet for 12 weeks. At the end of modeling, carotid color Doppler ultrasonography examination was performed to confirm which animal models were successfully induced with CAS, excluding model rabbits without typical CAS at the same time. Then, MPQ was applied on rabbits in the CAS-MPQ and the normal-MPQ groups for 3 weeks. By contrast, rabbits in the other 2 groups were fed normally without MPQ. Uniaxial failure tests were later performed on carotid arteries in all 4 groups, and at the end of the study, a 2-way factorial analysis of variance of the results was conducted. Results(1) At the end of modeling, 10 rabbits in the CAS-MPQ group and 9 in the CAS group were included with typical carotid atherosclerotic characteristics. (2) Young’s elastic modulus of the rabbit carotid artery increased more significantly in the CAS-MPQ group than the CAS group. (3) Compared with normal rabbit carotid arteries, atherosclerotic carotid arteries had lower levels of ultimate stress and ultimate strain but higher levels of ultimate load. ConclusionsThe uniaxial tensile mechanical properties of the rabbit atherosclerotic carotid artery were impaired after MPQ.

The effect of grain size on the deformation mechanisms and mechanical properties of polycrystalline TiN: A molecular dynamics study

The uniaxial tensile mechanical properties of polycrystalline TiN with 14 different grain sizes measuring 2.0–5.8 nm were studied via molecular dynamics with the second-nearest-neighbour modified embedded-atom method (2NN MEAM). The results show that the grain size affects the movement mechanisms of the grains and grain boundaries, and the relationship between grain size and tensile yield strength. The direct and inverse Hall-Petch formula of TiN are given. The dislocation migration of grain boundaries is the main deformation mechanism when the grain size is larger than 3.2 nm. When grains are smaller than 3.2 nm, grain rotation and grain boundary sliding are the preferred deformation mechanisms, which cause an inverse Hall–Petch effect. Polycrystalline TiN is at its hardest when the grain size ranges from 3 to 4 nm. The results can serve as theoretical basis for further doping non-metallic elements with critical grain sizes in the grain boundary produce superhard TiN composites.

Low cycle fatigue behaviors of pure Mo and Mo-La2O3 alloys

Pure molybdenum (PM) and La2O3 dispersion strengthened Mo alloy (ODS-Mo) were prepared by powder metallurgy through two different mixing method (solid-solid or SS mixing and solid-liquid or SL mixing). After annealed at 1050°C for 1h, the PM, SS-Mo and SL-Mo were compared in microstructure and mechanical properties. The microstructural examinations showed that the PM was mostly recrystallized with rather coarse grains, but the ODS-Mo alloys remained fine elongated grains. This discrepancy is due to a higher recrystallization temperature held in the ODS-Mo alloys. The uniaxial testing results showed that the ODS-Mo had higher tensile mechanical properties compared to the PM, which are attributed to the remarkable strengthening and ductilizing effect induced by the La2O3 particles. The low cycle fatigue (LCF) testing results revealed that the PM experienced cyclic hardening behaviors, while the ODS-Mo alloys exhibited cyclic softening behaviors. The Basquin-Manson-Coffin analyses results demonstrated that the ODS-Mo possessed a higher fatigue ductility and longer fatigue life than the PM. Two kinds of cracks, i.e., cleavage cracks and intergranular cracks, were experimentally observed to coexist on the fracture surface. In particular in the SL-Mo alloy, the two crack interacted and propagated forward until final fracture, leading to a step-like crack growth path and concomitantly enhanced fatigue ductility. In addition, different cycling dislocation structures were revealed between the PM and ODS-Mo alloys. Cycle fatigue mechanisms responsible for the fatigue behaviors and microstructure evolution during LCF testing were discussed. The best LCF resistance combined with superior uniaxial tensile mechanical properties found in the SL-Mo alloy were rationalized.

Viscoelastic behavior of carboxyl-terminated (butadiene-co-acrylonitrile)-based composite propellant binder containing polyglycidyl-type bonding agent

The influence of tris(2,3-epoxypropyl) isocyanurate as bonding agent on the physico-chemical, viscoelastic and uniaxial tensile mechanical properties of carboxyl-terminated (butadiene-co-acrylonitrile) cured with the polyglycidyl ether of glycerol and epichlorhydrin was investigated. Cross-link density values were estimated by swelling measurement. Temperature and frequency dependencies of rheological behaviour parameters (storage modulus, loss modulus, loss factor and glass-rubber transition temperature) were also analyzed. Based on the frequency dependencies of storage modulus, put in the range of temperature from -50 ?C to 20 ?C by the experiment, master curves (logG' vs log ?) were generated, reaching broader frequency interval in comparison to that used in the measurements. By choosing the glass-rubber transition temperature to be the reference one, Williams-Landel-Ferry equation constants were determined. Further, material constants, fractional free volume at the glass-rubber transition temperature and thermal coefficient of free volume expansion were calculated. Although small quantity of tris(2,3-epoxypropyl) affects the network density, the dynamic mechanical analysis showed that the bonding agent content did not affect the glass-rubber transition temperature of the tested materials.

Molecular aggregation structure evolution during stretching of environmentally benign lysine-based segmented poly(urethane-urea)s

The molecular aggregation structure evolution during uniaxial stretching deformation and the uniaxial tensile mechanical properties for an environmentally benign and biodegradable segmented poly(urethane-urea) (SPUU) elastomer based on an α-amino acid lysine-based diisocyanate (LDI) was investigated. The performance was compared with a conventional SPUU elastomer consisting of a symmetric aliphatic short chain diisocyanate (1,4-butane diisocyanate). Both SPUUs contain a 1,4-butanediamine chain extender and poly(ε-caprolactone) soft segments. The evolution of molecular aggregation structure during stretching was monitored using in-situ simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction. The LDI-based SPUU film contains weakly aggregated, disordered hard segment domains that readily dissociate upon mechanical deformation. The permanent deformation through fragmentation of the hard segment domains and strain-induced crystallization are associated with the low strength and large hysteresis loss of the LDI-based SPUU.

Promising PLA‐functionalized MWCNT composites to use in nanotechnology

Films based on polylactic acid (PLA) reinforced with multi‐walled carbon nanotubes (MWCNT) were developed after using an excellent methodology to ensure an optimum dispersion of the filler in the matrix. The functionalization of MWCNT was carried out through a Fenton reaction to generate hydroxyl (OH) and carboxyl (COOH) groups on their walls. After that, COOH groups were lengthened by reacting with thionyl chloride and then with triethylene glycol to achieve a terminal OH distanced from the wall of the MWCNT. Nanocomposites based on PLA containing different concentrations of functionalized filler (fMWCNT: 0.026, 0.10, and 0.18 wt%) were prepared by casting. The influence of filler concentration was investigated using some techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), water vapor permeability (WVP) and uniaxial tensile mechanical properties. Excellent dispersion of fMWCNT was observed suggesting that the technique of functionalization used was appropriate. All nanocomposites presented great stability, allowing them to be processed to temperatures reaching 300°C. Furthermore, an increasing trend of ultimate tensile strength (σu) up to 20% and a decrease of WVP around 40% with the addition of only 0.10 wt% of fMWCNT were obtained. Considering these results, the new biodegradable nanocomposites developed in this work could be very promising to replace synthetic plastics that currently are used in different areas such as nanotechnology, packaging and biomedicine. POLYM. COMPOS., 37:3066–3072, 2016. © 2015 Society of Plastics Engineers

Anisotropic tensile behavior of Ti–6Al–4V components fabricated with directed energy deposition additive manufacturing

The present work investigates the anisotropic mechanical properties of a Ti–6Al–4V three-dimensional cruciform component fabricated using a directed energy deposition additive manufacturing (AM) process. The mechanical properties of the component in longitudinal and transverse orientations with respect to the build layers were measured under uniaxial tension. While the average ultimate tensile strength of ∼1060MPa in both directions agrees well with prior studies on AM Ti–6Al–4V, the achieved elongations of 11% and 14% along the longitudinal and transverse directions, respectively, are higher. The enhanced ductility is partially attributed to the lack of pores present in these components. The anisotropy in ductility is attributed to the columnar prior-β grain morphology and the presence of grain boundary α, which serves as a path along which damage can preferentially accumulate, leading to fracture. In addition, the effect of oxygen on the strength and ductility of the component was studied. The findings indicate that a combined effect of an increase of 0.0124wt.% oxygen and a decrease in α-lath width due to differential cooling at different heights within the component resulted in an increase of ultimate and yield strengths without a significant loss of ductility. Furthermore, this study demonstrates that quasi-static uniaxial tensile mechanical properties similar to those of wrought Ti–6Al–4V can be produced in an AM component without the need for post-processing heat treatments.

Uniaxial tensile mechanical properties and model parameters determination of ethylene tetrafluoroethylene (ETFE) foils

This study concerns the uniaxial tensile mechanical properties and model parameters determination of ethylene tetrafluoroethylene (ETFE) foils used in structural engineering for membrane structures such as roofs and claddings. On one hand, a series of uniaxial tensile tests under a wide range of temperatures and constant loading speeds were conducted. The experimental results were processed with mathematical methods to determine the mechanical properties, such as first yield stress and elastic modulus. It is obtained that the first yield stress and elastic modulus decrease with increasing temperature but increase with the increasing loading speed. In detail, for the elastic modulus, the dimensionless ratio of the difference between the maximum and minimum values to the maximum value are 91% and 27% for temperature and loading speed tests; for the first yield stress, the dimensionless ratio are 82.9% and 19.2%, respectively. This indicates that the effect of temperature on mechanical properties is greater than that of loading speed when considering the normal working conditions.On the other hand, a constitutive model based on viscoelasticity–plasticity of semicrystalline polymers is employed for ETFE foils. The material parameters are determined with a numerical method based on the Runge–Kutta and least squares methods. The numerical results are in good agreement with the experimental results with a maximum deviation of 6.2%, demonstrating that this model could correctly predict the stress–strain relation of ETFE foils.

Atomistic simulations of pristine and defective hexagonal BN and SiC sheets under uniaxial tension

The uniaxial tensile mechanical properties of pristine and defective hexagonal boron nitride (BN) and silicon carbide (SiC) sheets are investigated through a molecular dynamics finite element method with Tersoff and Tersoff-like potentials. 2-Atom vacancy and 2 types of Stone–Wales defects are considered. It is found that uniaxial tensile stress–strain curves of defective and pristine sheets are almost identical up to fracture points. A centered single defect reduces significantly fracture stress and fracture strain from those of the corresponding pristine sheet. In contrast, Young׳s modulus is nearly unchanged by a single defect. One 2-atom vacancy in the sheet׳s center reduces 15–18% and 16–25% in fracture stress, and 32–34% and 32–48% in fracture strain of BN and SiC sheets, respectively. Reduction in fracture properties depends on the tensile direction as well as the orientation of Stone–Wales defects.