Theoretical Tensile Strength Research Articles

Effect of alloying element segregation on theoretical strength and structural low-energy transition of Ni grain boundaries: A first-principles computational tensile test study

Enhancing the stability and strength of nanocrystalline metals through the manipulation of grain boundary (GB) chemistry and structure is crucial for their engineering applications. In this study, first-principle computational tensile tests on Ni Σ5 [001] (210) GBs were conducted with considering Poisson's ratio and strengthening effect of alloying elements B, W, Zr, Ta, B-W and Zr-Ta segregation. The results indicate that the Zr-Ta co-segregated GB shows a remarkable increase in theoretical tensile strength by 195 % compared to the clean GB under small strain conditions. As tensile strain increases, both clean and segregated GBs undergo a low-energy structural transition from the Σ5 [001] (210) to the more stable Σ11 [110] (113). This work presents a promising approach for enhancing the stability of Ni nanograined materials through tensile deformation and GB segregation.

The first engineering application of 10MN CFRP cables in cable-stayed bridge in China

Existing engineering applications typically involve carbon fiber reinforced polymers (CFRP) cables with relatively small ultimate tensile forces (less than 10MN). This study presents the engineering application of China's first thousand-ton-grade CFRP cable-stayed bridge. The optimal steel and CFRP hybrid cable system was determined through a comparative analysis of structural behavior and life cycle cost. Thereafter, the CFRP cable, consisting of 121 strands of φ7 CFRP tendons, along with its anchoring system, was designed and manufactured with a theoretical ultimate tensile strength of 10,710 kN (Pb). Subsequently, the mechanical properties of 7–121 CFRP cable were investigated and experimentally verified. The tensile test revealed a satisfied ultimate tensile bearing capacity of 10,805 kN. Furthermore, after two million fatigue cycles, the CFRP cables retained approximately 90 % of their theoretical ultimate force, highlighting their excellent fatigue resistance. Besides, no damage occurred with a maintained tension force of 0.45 Pb at a temperature of 150 °C for a duration of at least 30 min, meeting the requirements of specification. Moreover, the key procedures of CFRP cable installation were also claimed. This study aims to further promote the application and development of CFRP cables in larger span and even super-long span bridges.

Local and global mechanical properties of orbital friction stir welding on API X65 PSL2 steel / Inconel 625 clad pipes

Orbital friction stir welding (FSW) is a promising approach to joining clad pipes. In this work, the influence of individual process parameters on the material flow even as, mechanical properties in orbital friction stir welded clad pipes is investigated. Due to the local heterogeneous microstructures within the weld, joints were evaluated by optical and scanning electron microscopy (SEM), microhardness, and digital image correlation (DIC). A microhardness increase was observed, with a maximum of 380 HV0.5 within the Inconel 625 and 265 HV0.5 within the X65 steel stir zones. Sound joints had an average ultimate tensile strength (UTS) exceeding up to 13% of the calculated theoretical tensile strength, which is obtained considering the minimum tensile strength of both materials. Additionally, failure occurred in the base material during the tensile testing, where the local strain in the stir zones of the X65 steel and Inconel 625 were only 3.3% and 10%, respectively. In summary, this investigation shows friction stir welded joints of API X65 steel and Inconel 625 clad pipes with high mechanical properties.

Structural evolution and mechanical response of multiple Al Σ5(210) grain boundaries with segregation of solute atoms: First-principles study

Grain boundary (GB) segregation of solute atoms is a key factor affecting the microstructure and macroscopic properties of materials. In this study, first-principles calculations were carried out to investigate the effect of solute atoms (Mg and Cu) segregation on the structural evolution and mechanical response of Al ground-state Σ5(210) GB (GB-Ⅰ) and metastable Σ5(210) GBs (GB-Ⅱ and GB-Ⅲ). The GB energy, segregation energy, and the theoretical tensile strength of the multiple Σ5(210) GBs were calculated. The results show that both Mg and Cu atoms tend to segregate in the boundary plane, thus reducing GB energy and improving GB stability. The segregation of Cu atoms reduced the GB energy more significantly than that of Mg atoms. The segregation of solute atoms can change the symmetric GB structure into an asymmetric one or induce GB phase transformation. The theoretical strength of GB-I is weaker than that of the metastable GB-II with higher GB energy, suggesting that grain boundaries with higher energy are not necessarily unstable. In addition, the effect of solute atom segregation on the GB strength depends not only on the type of element but also on the specific GB structure. The weakening effect of Mg segregation in GB-I and GB-II is due to the weak MgAl bond which enlarges the low charge density region of GB and increases the free volume of GB. The strengthening of GB-I and GB-II by Cu segregation mainly depends on the stronger AlCu bond than AlAl bond along the GB fracture path. The enhanced strength of GB-III with Mg and Cu segregation is attributed to the GB structural phase transformation caused by the segregation of solute atoms. The calculation results further elucidate the relationship between element segregation and grain boundary characteristics.

Study on the microstructure evolution and effect on mechanical properties of P92 steel during long term service

P92 heat-resistant steel is widely utilized in ultra-supercritical units due to its exceptional properties. This study examines the microstructure evolution and mechanical properties change of P92 during service spanning 0 to 93,000 h, while also exploring the correlation between microstructure changes and property variations. The results indicate that the matrix of P92 steel retains its characteristic tempered martensite structure, and the large-angle and small-angle grain boundaries in the steel remain nearly unchanged throughout extended service periods. However, the deterioration of P92 steel properties can mainly be attributed to alterations in precipitate size and martensitic lath width. The size of M23C6 and Laves particles increased from their initial dimensions of 150 nm and 0 nm to 260 nm and 370 nm, respectively. Moreover, the width of the martensitic lath increased from 350 nm to 700 nm. The martensitic lath contributes over 60 % of the theoretical tensile strength, playing a pivotal role in the exceptional strength of P92 steel during service. The presence of coarse Laves particles at the interface leads to a rapid reduction in impact energy, decreasing from approximately 130 J to 50 J, negatively affecting the impact energy of P92 steel.

An alternative method for predicting internal friction angle of rock materials

The shear strength properties of rock materials, cohesion and internal friction angle, are determined by carrying out tri-axial strength test on cylindrical core specimens in laboratory. But determination of these parameters by triaxial tests in accordance with standards and suggested methods, particularly for weak, fractured and weathered rocks is exteremely difficult and/or impossible due to difficulties related to preparation of test specimens suitable for this test. In addition, the tri-axial test requires high cost equipment and too much time for sample preparation and testing. In such cases, there is a need to precisely estimate the friction angle and estimation of rock shear strength properties using some indirect methods, as they are economical and easy to carry out. In this study, the traditional method, which is recommended to be used for the prediction of internal friction angle (ϕ) when triaxial test data is not available, was briefly assessed with its some limitations and an alternative method using theoretical tensile strength and uniaxial compressive strength to predict ϕ was proposed. Then the prediction performances of traditional and proposed methods were compared using a very large data set collected from published literature. The statistical reliability of the derived equations was assessed using F- and t-tests and according to the test results the prediction equations were found to be statistically reliable. The results indicated that the method proposed in this study using the theoretical tensile strength yields best predictions of ϕ when compared to those estimated from the traditional methods based on direct and Brazilian tensile strength values.

The Pt, Hf dopants in aluminide coating against S impurity: Dependence on grain boundary cohesion and energetic properties

The Pt and Hf additions in aluminide coating can pronouncedly change corrosion resistance against sulfur attack. To provide a comprehensive picture of this issue, by first-principles simulations we study the sulfur-induced embrittlement of ∑5(310)[001] symmetrical tilt grain boundary (STGB) in NiAl, with a focus on roles of Pt, Hf dopants played in sulfur-attacked grain boundary cohesion. The results show that the Hf-doping tends to increase GB combination with larger pre-breaker strength and theoretical tensile strength after sulfur introduction, while Pt-doping hardly makes contribution to the GB mechanical properties. The sulfur-induced embrittlement can be attributed to the charge density depletion and breaking of chemical bonding during stretching process, evaluated by the charge density distributions and bond length analysis. By analyzing the sulfur formation energy at NiAl bulk and NiAl(110) surface, we find that the presence of Pt enhances the energy criterion forming S impurity, while the significant reduction in adsorption energy after Hf-doping results from HfS strong atomic bonding. Alternatively, the existence of Pt decreases probability of S occurrence and becomes the barrier against S invasion. Instead, Hf tightly ‘embraces’ S impurity and impedes its diffusion into depth.

Reliability analysis of angle ply woven GFRP composite under in-plane loading condition using two parameter Weibull distribution

This study presents an analysis of the reliability of woven angle ply GFRP under both static and dynamic loading conditions. Hand lay-up technique was used to fabricate 8-ply laminates with four different fibre orientations (0°/90°, ±15°, ±30°, and ± 45°). The laminates were then tested for their tensile properties and fatigue behavior. When compared to specimens reinforced with different fibre orientations, specimens with (0°/90°) fibre orientation showed the highest failure stress and lowest failure strain. Theoretical model based on the Weibull distribution has been employed to determine theoretical tensile strength and mean fatigue life values for prepared laminates. Weibull parameters were used to generate S-N curves for various reliability levels (R = 0.10, 0.368, 0.50, and 0.99). The variation in the experimental results was investigated using the Weibull distribution function's shape factor (α) and coefficient of variance. These S-N curves were developed to assist designers in determining the first failure time as well as reliability and safety constraints. Finally, the study showed that the scatter value in all sample groups decreased to a failure criterion of approximately 106 cycles, and the scatter values were closer to each other.

New Insights on the Tensile Strength and Fracture Mechanism of c-ZrO2/α-Al2O3 Interfaces

The tensile strength and fracture properties of the c-ZrO2(001)/α-Al2O3(11¯02) interfaces were investigated by first-principle tensile simulations. Models with different stacking sequences of c-ZrO2(001) were examined. The theoretical tensile strength and work of adhesion were present. It was found that the adhesive strength of the interface was strongly influenced by the termination of c-ZrO2(001), and the c-ZrO2(001)/α-Al2O3(11¯02) interfaces adhered weakly. Then, variations of the atomic bonds were observed to clarify the fracture characteristics of the interfaces. Our study indicates that the fracture modes of the O- and Zr-model tend to be ductile fractures, while the fracture mode of the 2O-model is a brittle fracture. Furthermore, all three models were completely separated along the intermediate layer between the initial ZrO2 and Al2O3 slabs. Finally, we compared our results with those available in the published literature, and the potential application of the first-principle results will be further discussed.

Influence of the Hoek–Brown failure criterion with tensile strength cut-off on the roof stability in deep rock tunnels

The Hoek–Brown (HB) failure criterion provides reasonable estimates of the peak strength of isotropic rocks for shear failure; however, this is less so for tensile fractures. Hoek and Brown advised against the direct application of the HB criterion during excavation at deep depths and introduced a tension cut-off (TC) based on reliable extension test data. However, its influence on rock structures remains unclear, with no previous studies on safety assessment considering TC. In this study, a stability analysis of deep tunnel roofs was performed using the HB yield function with reduced or eliminated tensile strength. The parabolic form of the HB envelope was terminated using a circular arc in the tensile stress regime. Such a modification allows some part of the failure mechanism to be separated from the stationary rock with a large volumetric strain governed by the TC. The kinematic approach of limit analysis was utilized as the study approach. The computation results revealed that, among the two common tunnel cross-sections, rectangular tunnels were susceptible to the TC, i.e., the stability number with 10% of the theoretical tensile strength was more than twice that of the original envelope. Circular tunnel roofs can be self-supported even with a zero tensile strength (19% increase in the stability number) owing to the addition of a confining stress. For different HB constants, the relative increase in the stability number subjected to the TC was surprisingly consistent. The factor of safety, defined as the shear strength and required supporting pressure, was derived from the envelope with a TC.

Physical properties and tensile strength evolution of gypsum materials under different water content conditions

To investigate the physical properties and tensile strength evolution of gypsum materials under different water content conditions, three groups of gypsum standard samples were prepared, including natural, saturated and dehydrated gypsum samples. Electron microscopy, composition analysis, Brazilian splitting tests and numerical simulation analysis were carried out. The results are as follows. The larger the water content of the samples is, the higher the content of CaSO4·2H2O, the more flocculation structures on the surface, and the higher the longitudinal wave propagation speed. Saturation and dehydration change the composition of the sample and cause a change in its tensile strength and failure mode. The fitting effect of the modified Hoek-Brown criterion is obviously better than that of the modified Mohr-Coulomb criterion because it considers the influence of uniaxial compressive strength. The Balmer criterion introduces the index b and greatly improves its regression accuracy. The vertical compressive stress exhibits a concentrated distribution. At x = 0, the peak value of the vertical load appears at the two ends of contact between the specimen and the indenter and gradually decreases from both ends to the centre. The horizontal stress is mainly tensile stress, and the value at x = 0 is the theoretical tensile strength. It is uniformly distributed on the line directly affected by the vertical load and decreases to both ends of the specimen along the line. It is reduced to 0 at the left and right ends. The horizontal deformation arises from both sides of the disk tip and then spreads downwards in an arc during loading. The horizontal strain in the upper part of the disk is always larger than that in the lower part. The upper part reaches its tensile strength and then fails due to the continuous loading.

Mechanical properties and chemical bonding transitions of Nb/NbC and α-Fe/NbC interfaces in Fe-Nb-C composites

The metal/ceramic interface is of utmost significance for the study of alloyed steel containing niobium and in situ niobium carbide reinforced composites. Herein, first-principles calculations based on density functional theory (DFT) are carried out to study adhesion work (Wad), electronic structure, bonding property and theoretical tensile strength of two types of interfaces, i.e., Nb/NbC and α-Fe /NbC, in Fe-Nb-C composites. The effect of termination of two different atoms (Nb- and C-) in the interface and different interfacial positions on properties of Nb/NbC and α-Fe/NbC interfacial structures is studied in detail. The results reveal that the effect of both types of interfaces on the bulk phase is mainly concentrated in the first three-layers near the interface, and C-terminated interfaces exhibit stronger stability (7.60 J/m2) and greater theoretical tensile strength (0.80 J/m2) than what. After high-precision geometrical optimization, interfacial adhesion strength exhibits the following order: Nb(001)/NbC(010)> α-Fe(110)/NbC(010)> α-Fe(100)/NbC(100). In terms of interfacial bonding, it is found that both C-terminated interfaces exhibit strong covalent and ionic bonds, where Nb-C bonding is better than Fe-C bonding.

Studies on glass/epoxy and basalt/epoxy thin-walled pressure vessels subjected to internal pressure using ultrasonic ‘C’ scan technique

Fiber reinforced nanocomposite tubes are playing a vital role in the transportation of fluids in petrochemical industries, where these composite tubes store fluid under pressure. Therefore, it is important to estimate the amount of pressure that can be handled by the tubes and investigate the damage mechanisms of composite tubes using non-destructive testing techniques. In this work, mechanical properties and the pressure withstanding capability of different weight percentages (0, 0.5, 1 and 1.5 wt%) of silica nanoparticles added in glass/epoxy and basalt/epoxy composite tubes are investigated. Before performing these tests, the transmission electron microscopy (TEM) analysis was performed to ensure the uniform distribution of silica nanoparticles in the epoxy. Further, mechanical tests were carried out. The fractured surface of composites was analyzed using scanning electron microscopy (SEM). The Weibull modeling was used to predict the theoretical tensile, flexural and impact strength values. Further, hydrostatic pressure tests were performed, and then full-field damage assessments were performed using the ultrasonic ‘C’ scan. It was found that basalt/epoxy/silica nanocomposite tubes exhibited better mechanical and pressure withstanding capability, owing to the presence of higher amounts of iron and aluminum oxides, than their counterparts of glass/epoxy/silica nanocomposite tubes. Numerical analysis was also performed to confirm the allowable pressure limits of the composites under hydrostatic load. The failure of tubes has not occurred below allowable pressure values, which indicate good correlations with experimental results. The results of the study will help to design and manufacture composite tubes with better pressure withstanding capability at a reasonable cost.

Experimental and theoretical analysis of polymer blend composites using Weibull distribution

ABSTRACT In the present work, the mechanical and thermal behaviors of Poly Butylene Terephthalate, Poly Trimethylene Terephthalate and Poly Butylene Terephthalate (30% Glass filled) polymer and polymer blend composites were studied. Reliability analysis on tensile strength and flexural strength for the polymers and polymer blend composites at different cross-head speeds was done by Weibull distribution methodology. By using Weibull distribution (Two parameters), the theoretical tensile and flexural strength values were determined for the polymers and polymer blend composites at different cross-head speeds. Weibull analysis revealed good correlation between experimental mechanical strength values at varying load conditions with uniform strength distribution. The probability functions indicated good correlation between the cumulative density and strength of the polymer blends suggesting improved thermal stability and reduction in loss of material mass. A thermal scan to determine the the mass loss, glass transition temperature (Tg), melting and decomposition, revealed improved adhesion and enhanced constituent miscibility while the fractography indicated increased interfacial bonding strength and reduced phase tension. The improved adhesion between the polymer phases was caused by the compatibilizer which also improved the mechanical properties and thermal stability.

Optimization of FDM 3D printing parameters for high strength PEEK using the Taguchi method and experimental validation

PurposePolyetheretherketone (PEEK) is used to manufacture biomedical implants because it has a high strength-to-weight ratio and high strength and is biocompatible. However, the use of fused deposition modeling to print a PEEK results in low strength and crystallinity. This study aims to use the Taguchi method to optimize the printing factors to obtain the highest tensile strength of the printed PEEK object. The annealing effect on printed PEEK object and crystallinity are also investigated.Design/methodology/approachThis study determines the printing factors including the printing speed, layer thickness, printing temperature and extrusion width. Taguchi experimental design with a L9 orthogonal array is used to print the tensile specimen and carried out the tensile test to compare the tensile strength and porosity. Analysis of variance (ANOVA) is used to determine the experimental error and to determine the optimization printing parameters to obtain the highest tensile strength. A multivariate linear regression analysis is used to obtain the linear regression equation for predicting the theoretical tensile strength. An X-ray analysis is achieved to evaluate the crystalline of printed object. The effect of annealing is investigated to improve the tensile strength of printed part. An intervertebral lumber device is printed to demonstrate the feasibility of the obtained optimization parameters for practical application.FindingsTaguchi experiment designs nine sets of parameters to print the PEEK tensile specimen. The experimental results and the ANOVA present that the order in which the factors affect the tensile strength for printed PEEK parts is the layer thickness, the extrusion width, the printing speed and the printing temperature. The optimized printing parameters are a printing speed of 5 mm/s, a layer thickness of 0.1 mm, a printing temperature of 395 °C and an extrusion strand width of 0.44 mm. The average tensile strength of printed specimen with the optimized printing parameters is 91.48 MPa, which is slightly less than the theoretical predicted value of 94.34 MPa. After annealing, the tensile strength increases to 98.85 MPa, which is comparable to that for molded PEEK and the porosity decreases to 0.3 from 3.9%. X-ray diffraction results show that all printed and annealed specimens have a high degree of crystallinity. The printed intervertebral lumber device has ultimate compressive load of 13.42 kN.Originality/valueThe optimized printing parameters is suitable for low-price fused deposition modeling machine because it does not involve a table at high temperature and can print the PEEK object with high tensile strength and good crystalline. Annealing parameters offer a good solution for tensile strength improvement.

Tensile mechanical behavior and failure mechanisms of fiber metal laminates under various temperature environments

This paper mainly investigates the tensile behavior of fiber metal laminates (FMLs) under various temperatures ranged from 25 ℃ to 175 ℃ combined experimental measurement, theoretical model and numerical technique. Firstly, based on numerous tensile tests under various temperatures, different tensile load–displacement response and damage modes for FMLs can be obtained and compared. And in virtue of the scanning electron microscopy (SEM), microscopic damage modes are identified through the fracture surface scanning of FMLs subjected to different temperatures. Subsequently, in order to analyze the discreteness of experimental results and evaluate the theoretical tensile strength of FMLs under different temperatures, the two-parameter Weibull statistics model is established for engineering application of FMLs. Finally, the effect of layer direction on damage modes and progressive damage evolution process of FMLs is characterized numerically. These results indicate that the tensile strength of FMLs represents a nonlinear downward trend with the increase of temperature. The complex failure mechanisms under different temperatures can be captured from SEM observation, including fiber/matrix debonding, fiber pull-out, matrix microcrack, delamination damage and so on. The deeper understanding of tensile behavior and failure mechanisms of FMLs under thermal conditions can be provided for the design and utilization of FML structures.

Hardened wood as a renewable alternative to steel and plastic

Hardened wood as a renewable alternative to steel and plastic

Interface modulation mechanism of alloying elements on the interface interaction and mechanical properties of graphene/copper composites

The interface doping with transition metal elements (TM = Ti, Cr, Co, Ni) has been experimentally proved to be an effective pathway to improve the weak interface bonding of graphene/copper (Gr/Cu) composites. In this paper, the microscopic influencing mechanism of TM doping on the interface interaction and mechanical properties of Gr/Cu was investigated by the first-principles calculations. The sandwich model with graphene embedded in Cu matrix was adopted here to simulate the TM-doped interfaces. It is revealed that the introduction of TM doping elements can significantly improve the work of separation, which relates to the electronegativity difference between TM and Cu elements based on the analysis of the interface electronic structure. Then, the mechanical properties of the clean and TM-doped interfaces were studied by the rigid stretching and the relaxed stretching. We found that, in rigid case, the theoretical tensile strengths of different interfaces are positively correlated with the work of separation, and the electronegativity is also a main factor affecting the mechanical properties. Furthermore, a fitting function containing the element electronegativity was applied to get the stress–strain relationship curve, and the quantitative relationship between the interface bonding and mechanical properties determined in this work can be served as a favorable support for the experimental design of Gr/Cu composites.

The Use of STEM Approaches To Improve Formula Derivation Steps in Material Science and Engineering Programmes at Higher Education Institutions

Many complex formula derivation steps found within material science and engineering programmes are essential skill-developing activities that enhance students’ learning. However, most students lack the required mathematical knowledge to fully comprehend some of those derivation steps. This work developed a framework of clarifying some of the formula derivations steps by adding further mathematical steps that support the students’ constructive and cognitive learning. Some derivation steps were added to the derivations of the theoretical tensile strength model as well as the Maxwell’s and the Voigt-Kelvin models. The idea was not to disrupt students’ constructive or cognitive learning processes but to facilitate their learning since their ultimate aim is not to derive but to apply the steps of the modified derivations in solving other material science and engineering problems. The students benefited from the activities in two folds; firstly, they understood the reasons behind each derivation step and secondly, it improved their self-study activities by reducing their study periods. These activities provide a platform to widen STEM activities at higher education institutions. The ongoing work will look at other important formula derivation steps within material science and engineering that can enhance students’ learning.

On the effects of temperature on tensile behavior of carbon fiber reinforced epoxy laminates

As a highly promising lightweight material, carbon fiber reinforced plastics (CFRP) composites have been widely used in aerospace, marine and automotive industries, which could expose to low or high thermal environments with varying material properties. This study investigated the effects of temperature variation ranging from −30 °C to 160 °C on tensile properties of CFRP experimentally and theoretically. The specimens were prepared using thermo-forming technology; and the glass transition temperatures of epoxy resins were measured by dynamic mechanical analysis (DMA). Digital image correlation (DIC) technique was used to capture the variation in strain and damage fields. By means of scanning electron microscopy (SEM), the failure mechanisms, delamination and resin softening, were identified by scrutinizing the images of fracture areas subject to different temperatures. The two-parameter Weibull analysis was conducted to evaluate the theoretical tensile strengths from relatively discrete data. The obtained Weibull parameters are considered useful for the reliability analysis of CFRP structures. It is found that the tensile strength decreases with the increase of temperature in a nonlinear fashion, which can be modeled in terms of a tanh function by correlating with the temperature-dependent experimental data. The study is anticipated to provide fundamental understanding and a predictive tool for mechanical strength of composite structures operating under different thermal conditions.