Tensile Fracture Toughness Research Articles

Molecular insights into strengthening of biomineral apatite with carbon nanofillers: A simulation study

Biomineral apatite (Ap) has been widely utilized in clinical bone graft procedures for over 25 years. However, its lower tensile strength and fracture toughness compared to natural bone limit its application in large load-bearing systems. This approach aims to enhance the mechanical performance of Ap while preserving its bioactivity, thereby expanding its potential clinical applications. In this study, the creation and processing of carbon nanofiller-based Ap nanocomposites, including pristine and vacancy-defective carbon nanofillers, are investigated using molecular dynamics simulations. The mechanical behaviour of Ap nanocomposites reinforced with three types of carbon nanofillers (CNF) is examined: (i) three-dimensional metallic carbon nanostructure with interlocking hexagons T6B (beam-like), (ii) carbon nanotubes (CNT), and (iii) three-dimensional metallic carbon nanostructure with interlocking hexagons T6P (plate-like). The analysis encompasses detailing the methodology utilized for modelling the equilibrated structures of CNF/Ap nanocomposites, along with the characterization of their elastic parameters. Computational findings reveal the significant impact of CNT chirality, Aspect Ratio (AR) of T6B and orientation of T6P on the mechanical properties of the nanocomposites and observed inclusion of CNF enhances the mechanical properties compared with those of pure Ap. The findings indicate that the lower diameter CNT and smaller cross-sectional area of T6B exhibit higher tensile strength compared to the larger CNT diameter and larger cross-sectional area of T6B of the same length. Further, the analysis highlights the substantial influence of vacancy defects concentration on CNF on the mechanical behaviour of nanocomposites, with an increase in defects correlating to a decrease in the mechanical strength of both CNF and CNF-based nanocomposites.

Research on Crack Propagation of Nitrate Ester Plasticized Polyether Propellant: Experiments and Simulation.

To understand the fracture properties of the nitrate ester plasticized polyether (NEPE) propellant, single-edge notched tension (SENT) tests were carried out at room temperature (20 °C) under different tensile rates (10-500 mm/min). The mechanical response, crack morphology, evolution path, and crack propagation velocity during the fracture process were studied using a combination of a drawing machine and a high-speed camera. The mode I critical stress intensity factor KIc was calculated to analyze the tensile fracture toughness of the NEPE propellant, and a criterion related to KIc was proposed as a means of determining whether the solid rocket motors can normally work. The experimental results demonstrated that the NEPE propellant exhibited blunting fracture phenomena during crack propagation, resulting in fluctuating crack propagation velocity. The fracture toughness of the NEPE propellant exhibited clear rate dependence. When the tensile rate increased from 10 mm/min to 500 mm/min, the magnitude of the critical stress intensity factor increased by 62.3%. Moreover, numerical studies based on bond-based peridynamic (BBPD) were performed by modeling the fracture process of the NEPE propellant, including the crack propagation speed and the load-displacement curve of the NEPE propellant. The simulation results were then compared with the experiments.

Impact of Alumina-Based Binder on Formation of Dense Strontium Zirconate Ceramics

Strontium zirconate (SrZrO3) is a technical ceramic with potential for refractory applications due to its chemical stability at high temperatures, high melting temperature, and favourable thermal expansion coefficient. Practical use of SrZrO3 is limited by poor mechanical strength relative to ceramics such as alumina (Al2O3). Sintering of SrZrO3 with a hydratable Al2O3 binder is investigated as a method for improving mechanical performance. Density, phase composition, thermomechanical properties, and chemical stability in contact with alloys up to 1350°C are considered. Results are compared with SrZrO3 samples formed using a traditional polyvinyl alcohol (PVA) binder. SrZrO3 reacts with alumina during sintering to form SrAl2O4 and ZrO2. Compared to the PVA binder, the alumina binder drastically reduced porosity in the ceramic, while increasing the indirect tensile strength and fracture toughness. No significant detriment to thermal expansion or chemical stability was found, offering potential for high-temperature applications particularly as a dense crucible material.

Strength and Fracture Toughness of Type 304 and 316 Austenitic Stainless Steels at 4.2 K

The tensile properties and fracture toughness of type 304L, 316L and 316LN austenitic stainless steels and their weldments at cryogenic temperatures have been summarized in the literature. Rolled plates showed a trade-off relationship between 0.2% proof stress and planestrain fracture toughness with those at 4.2 K. The 0.2% proof stress increases with increasing C+N content, and the fracture toughness depends on their austenite stability to α’-martensitic transformation at the crack tip. The formation of shear bands at low strains is directly related to fracture toughness. The stacking fault energy represents the shear-band formation as well as slip deformation manner, so alloy design with higher Ni, Mn, and Mo contents in the chemical composition range of 316LN would be desirable to improve fracture toughness due to higher stacking fault energy.

A new type of shale gas reservoir—carbonate-rich shale: From laboratory mechanical characterization to field stimulation strategy

Recently, a new promising type of marine shale gas reservoir, carbonate-rich shale, has been discovered. But the mechanical properties of this type of shale were still unrevealed and the corresponding reservoir stimulation design was lack of guidance. Using the deep downhole cores of an exploratory carbonate-rich shale gas well, the physical and mechanical parameters and failure mechanism of the whole reservoir section were acquired and evaluated systematically, by performing XRD, tri-axial compression, Brazilian splitting, and fracture toughness tests. A new model was established to evaluate the reservoir brittleness based on fracture morphology and stress-strain curve. Recommended strategy for reservoir stimulation was discussed. Results showed that (1) Carbonate-rich shale possessed high compressive strength and high Young's modulus, which were improved by 10.74% and 3.37% compared to that of siliceous shale. It featured high tensile strength and fracture toughness, with insignificant anisotropy. (2) With the content of carbonate minerals increasing, the shear failure morphology transformed from sparse and wide brittle fractures to diffusely distributed and subtle plastic cracks. (3) The brittleness index order was: siliceous shale, clay-rich shale, carbonate-rich shale, and limestone. (4) The special properties of carbonate-rich shale were rooted in the inherent feature of carbonate minerals (high strength, high elastic modulus, and cleavage structure), resulting in greater challenge in reservoirs stimulation. The above findings would promote the understanding of carbonate-rich shale reservoirs and provide reference for the optimum design of reservoir stimulation.

Strain-Based damage model for ductile tearing simulation under combined tensile and shear modes

This paper proposes a strain-based damage model to simulate ductile tearing under combined tensile and shear modes. For tensile mode, the multiaxial fracture strain model depending only on the stress triaxiality is used, determined by analysing smooth bar tensile test and fracture toughness test data. For shear mode, a simple constant fracture strain model is used, determined by analysing smooth bar torsion test and torsion fracture test using a deep surface cracked cylinder specimen. The proposed damage model is applied to simulate circumferential surface cracked pipe made of SUS 304 under combined bending and torsion. Comparison with full-scale surface cracked pipe test data suggests that the use of the combined tensile and shear damage model with the linear interaction rule gives good and conservative prediction results.

Influence of Oxygen/Argon/Nitrogen multi-component plasma modification on interlayer toughening of UHMWPE fiber reinforced composites

The study reveals the influence of glow discharged three gas sources of Oxygen/Argon/Nitrogen plasma modification on interlayer toughening of ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced composite. The failure modes under bending, tensile and interlayer fracture toughness testing were analyzed through acoustic emission (AE) technology. The results showed that Oxygen/Argon/Nitrogen multi-component plasma modified fiber introduced more hydrophilic groups such as hydrogen and hydroxyl groups, and significantly enhanced the binding of fiber and matrix. The GⅠC (Mode-I interlaminar fracture toughness) of multi-component plasma modified composites exhibited increased by 61.67 %, 40.88 % and 18.01 % compared to untreated, Oxygen and Oxygen/Argon plasma, respectively, while GⅡC (Mode-II interlaminar fracture toughness) increased by 38.57 %, 25.57 % and 23.09 %. AE cluster analysis exhibited that multi-component plasma modified composites formed an energy dissipation mechanism dominated by fiber breakage. Additionally, the oxygen, argon, and nitrogen plasma modification have a synergistic effect on interlayer toughening.

Bioinspired helical fiber/elastomer composites with high strength

For general composites, fiber can improve the strength of rubber matrix, but it will damage the original high deformation that affect the toughness. Therefore, to solve this problem, we propose a strategy of constructing rubber-helical fiber composite, which can not only improve the strength of rubber, but also maintain the original high deformation of rubber. Inspired by helical structure in nature, we convert straight fibers into helical fibers by winding. The helical fibers with spring characteristic have high strength and large deformation matching with rubber. The tensile strength and fracture toughness of the composite are 3.51 and 3.41 times those of the rubber matrix, respectively. When the aramid fiber was used instead of nylon fiber, the strength of the composite is 12.81 MPa, which is 17.8 times that of pure rubber matrix, and the mass fraction of the fiber is only about 1.60 %. Furthermore, by analyzing the reinforcement and toughening effect of helical fiber, we have determined that helical fiber plays the role of bearing stress and dispersing stress into three-dimensional space in composites.

Experimental evaluation of bamboo natural fiber composite reinforced with SiO2 nanoparticles for aircraft applications

PurposeComposite materials have revolutionized the aerospace industry by offering superior structural qualities over traditional elements. This study aims to focus on the development and testing of bamboo natural fiber-based composites enhanced with SiO2 nanoparticles.Design/methodology/approachThe investigation involved fabricating specimens with varying nanoparticle compositions (0, 10 and 20%) and conducting tensile, flexural, impact and fracture toughness tests. Results indicated significant improvements in mechanical properties with the addition of nanoparticles, particularly at a 10% composition level.FindingsThis study underscores the potential of natural fiber composites, highlighting their environmental friendliness, cost-effectiveness and improved structural properties when reinforced with nanoparticles. The findings suggest an optimal ratio for nanoparticle integration, emphasizing the critical role of precise mixing proportions in achieving superior composite performance.Originality/valueThe tensile strength, flexural strength, impact resistance and fracture toughness exhibited notable enhancements compared with the 0 and 20% nanoparticle compositions. The 10% composition showed the most promising outcomes, showcasing increased strength across all parameters.

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy.

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy's behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m1/2, which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

Rapid evaluation of trade-offs between strength and impact toughness of wheel steels by instrumented spherical indentation test

In this paper, an improved size-independent instrumented spherical indentation test (ISIT) method was proposed to determine tensile strength and fracture toughness on wheel rims of two different types of wheel steels. Additionally, Charpy impact specimens were taken from three specific positions on the wheel rims and subjected to standard Charpy impact testing. The resulting Charpy impact energy (CVN) were matched with the fracture toughness measured by ISIT (KIc,IT) at the same positions. There was a clear linear correlation between CVN and the square of KIc,IT, which was consistent with the established relationship between both properties as determined by conventional Charpy impact and compact tension tests. Therefore, we expanded the ISIT method to study the impact of cooling rates on the variation of yield strength and Charpy impact energy across the wheel rim. To accomplish this, we designated additional testing points on the wheel rim using the ISIT method. The investigation found trade-offs between strength and impact toughness of wheel steels under different cooling rates. The above findings demonstrated the effectiveness of using the ISIT method, which facilitated high-resolution fracture toughness measurement, to establish accurate correlation between CVN and fracture toughness of wheel steels. Moreover, this ISIT method can be employed to regulate heat treatment of material properties to meet specific application requirements.

Effects of Co on the microstructure evolution and mechanical properties of Ti-4Al-6Cr-5Mo-8 Nb alloy by ultrasonic vacuum melting

An investigation was conducted into the impact of low cobalt content on the microstructure and mechanical properties of titanium alloys. Ti-4Al-6Cr-5Mo-8 Nb-xCo (x = 0, 2, 3, 4, and 5) alloys were prepared by ultrasonic-assisted melting and casting. The changes in microstructure, mechanical properties, and the strengthening and toughening mechanisms were researched. Results show that, when the cobalt content increases from 0 to 5 wt%, the as-cast structure is all β phase. The lattice parameter of the β phase decreases from 0.3663 to 0.3114 nm, a 15% decrease. The size of primary β grains decreases from 676.8 to 310.7 μm, a 54% decrease. When the cobalt content exceeds 3 wt%, the segregation energy of cobalt increases and grain boundary segregation occurs. Grain refinement is due to constitutional supercooling caused by the β-stable element cobalt, as well as the solute drag caused by the differences in intragranular and grain boundary compositions. In addition, the size mismatch between cobalt and titanium atoms leads to lattice distortion. As the cobalt content increases from 0 to 3 wt%, the tensile strength increases from 918.1 to 1147.8 MPa, a 25% increase, while the fracture toughness increases from 51.7 to 59.7 MPa·m1/2, a 15% increase. At 5 wt% cobalt, the tensile strength and fracture toughness diminished to 247.5 MPa and 14.8 MPa·m1/2, respectively. The decrease in lattice parameters mainly lead to an increase in strength. The secondary crack leads to an increase in toughness. The decline in strength and toughness results from cobalt segregating at grain boundaries, leading to embrittlement.

Effect of loading direction and anatomical location on the ultimate tensile stress, fracture toughness, and failure patterns of knee meniscus

BackgroundRupture of the knee menisci is a common injury that can have implications for other conditions, such as osteoarthritis. The fracture toughness of soft tissue (Jc) is a mechanical property that characterizes its resistance to tear extension. To date, Jc of the meniscus has not been quantified. MethodsCyclic tensile tests were conducted on meniscus samples to determine Jc and explore its characteristics. Initially, the study investigated the impact of an initial notch on the ultimate tensile stress. This allowed for an understanding of how the presence of a notch affects its structural integrity. Subsequently, Jc was measured in both the radial and circumferential directions to assess its loading direction dependency. Furthermore, the study assessed the effect of anatomical location by comparing samples collected from the femoral and tibial layers. ResultsDefect tolerance of the meniscus is influenced by the loading direction. In the circumferential direction, the presence of an initial notch did not affect the ultimate stress, and no crack expansion was observed. In radial samples with a notch length of 40% or more of the total width, crack propagation occurred, leading to a decrease in the ultimate stress (p< 0.01). Additionally, Jc was found to be higher in the femoral layer compared to the tibial layer (p= 0.017). ConclusionThe study also examined the failure patterns of the meniscus to enhance our understanding of its pathology. These insights contribute to a better comprehension of meniscus injuries and can aid in the development of more effective treatment strategies.

Influence of structural geometry on tensile properties and fracture toughness in 3D printed novel structures

The study employed chopped fiber-reinforced nylon composite, referred to as “Onyx,” along with continuous carbon fiber materials. Using the material extrusion manufacturing process, three sandwich structures were created: a conventional, a concave hexagonal with negative Poisson's ratio, and a feather-inspired structure. Tensile testing and finite element simulations were conducted to analyze their tensile properties and crack propagation paths under tension. Fractal dimensions were calculated for each structure: the standard structure had a dimension of 1.4626, the bionic feather-inspired was 1.4810, and the negative Poisson's ratio concave hexagonal structure measured 1.4973.

Enhancing carbon fiber reinforced aluminum laminates with cellulose paper interlayers: experimental characterization of tensile, flexural, and interlaminar fracture toughness

ABSTRACT The mechanical properties of fiber metal laminates (FML) are influenced by several various factors. Interface adhesion plays a particularly crucial role in interlaminar strength. Enhancing the interlaminar strength of carbon fiber reinforced aluminum laminate (CARALL) composites present a persistent challenge due to inherent weaknesses between metal and composite elements. Therefore, this study focuses on improving the interlaminar performance of CARALL composites by introducing cellulose paper interlayer at the metal/composite interface. The cellulose paper interlayer offers the advantage of being cost-effective and sustainable. Cellulose paper-interleaved CARALL composites were fabricated by vacuum bagging method and exhibited noteworthy improvements in mechanical properties. Comparative analysis with pristine samples revealed substantial enhancements, including a 15% increase in tensile strength, a remarkable 42% improvement in flexural strength, and a significant enhancement in mode-I fracture toughness by 65%. Furthermore, the cellulose paper interleaving played a crucial role in stabilizing fracture formation at the fiber-matrix interface, with mode II fracture toughness witnessing a 3% increase. Visual examination revealed the underlying toughening processes occurring in the interfacial area. This innovative approach of interleaving laminated composites with cellulose paper emerges as a sustainable and effective strategy, demonstrating the potential to fortify and toughen the interlaminar zones of CARALL composites.

A novel fracture criterion for elastic‐brittle cracked body under compression and shear conditions

AbstractWhen the elastic‐brittle cracked body is subjected to compressive‐shear loading, not only does the phenomenon of wing crack initiation and propagation occur, but there is also a notable incidence of secondary crack initiation and propagation due to shear stress. Moreover, the shear fracture toughness (KIIc) predicted by the fracture criterion in the framework of classical fracture mechanics is usually smaller than the tensile fracture toughness (KIc), which is inconsistent with the actual observations. Therefore, this research firstly establishes a mechanical model of an elastic‐brittle cracked body under biaxial compression considering three kinds of crack parameters and materials' mechanical properties. Then, the stress field characteristics at the crack tip are analyzed. Next, a compression‐shear mixed fracture criterion is proposed. Finally, the effects of the lateral pressure coefficient (λ), critical plastic zone size (rc), friction coefficient (f), and deformation parameters of the crack surface on the failure modes at the crack tip are investigated.

Closed-form fracture model for evaluating crack resistance of 3D printed fiber-reinforced alkali-activated slag/fly ash recycled sand concrete

To reduce resource consumption and greenhouse gas emissions, 3D printed alkali-activated slag/fly ash recycled sand (RS) concrete (3DP AARSC) was developed in this paper. The reasonable evaluation of its crack resistance is crucial to structural safety and stability since steel bars are still difficult to embed in 3DP samples automatically so far. The realistic fracture parameters can be responsible for the reasonable evaluation and are extremely difficult to predict accurately based on traditional methods unless the specimen sizes are large enough. Therefore, the purpose of this study is to determine the size-independent tensile strength (ft) and fracture toughness (KIC) through a predictive fracture model incorporating the heterogeneity and discontinuity of 3DP AARSC. First, fracture tests of small-sized specimens were conducted to clarify the fracture mechanisms of 3DP AARSC in different loading directions. Subsequently, based on the boundary effect model, the size-independent ft and KIC were explicitly correlated to the maximum fracture load (Fmax) in different loading directions and directly obtained if Fmax was measured from the tests. The results displayed that the predicted ft and KIC of 3DP AARSC loaded perpendicular to the printing direction were significantly higher than the counterparts of concrete loaded parallel to the printing direction by 108.7% at most. The greatest cracking resistance was demonstrated in the specimens with the RS replacement rate of 60% for natural river sand (NS), resulting in the maximum increase of 19.9% in ft and KIC compared with the 3DP concrete with 100% NS. The fiber addition and partial RS replacement increased the difference in the crack resistance along various loading directions. Moreover, the fiber incorporation had no significant improvement in the crack resistance of 3DP AARSC loaded parallel to the printing direction and apparently increased its ft and KIC along other loading directions.

Mechanical Properties and Ion Release from Fibre-Reinforced Glass Ionomer Cement.

The aim of this study was to compare the mechanical properties and ion release from a commercially available resin-modified glass ionomer cement to a formulation reinforced by the addition of short glass fibres at various percentages. Methods: Three experimental groups were prepared by adding a mass ratio of 10%, 15% and 20% of short glass fibres to the powder portion of the cement from a capsule (GC Fuji II LC), while the control group contained no fibres. Microhardness (n = 12), fracture toughness, and flexural, compressive and diametral tensile strength (n = 8) were evaluated. To study ion release, readings were obtained utilising fluoro-selective and calcium-selective electrodes after 24 h, 7 days and 30 days (n = 12). The spatial distribution of fibres within the material was evaluated through scanning electron microscopy. The data were analysed using one-way ANOVA with a Bonferroni adjustment. Results: The findings suggest that elevating fibre weight ratios to 20 wt% results in improved mechanical properties (p < 0.05) in microhardness, flexural strength, diametral tensile strength and fracture toughness. In terms of ion release, a statistically significant difference (p < 0.001) was observed between the groups at the conclusion of 24 h and 7 days, when the fluoride release was much higher in the control group. However, after 30 days, no significant distinction among the groups was identified (p > 0.05). Regarding calcium release, no statistically significant differences were observed among the groups at any of the evaluated time points (p > 0.05). SEM showed the fibres were homogeneously incorporated into the cement in all experimental groups. Conclusions: Resin-modified glass ionomer enhanced with short glass fibres at a weight loading of 20% showcased the most favourable mechanical properties while concurrently maintaining the ability to release fluoride and calcium after a 30-day period.

Assessment of tensile deformation and fracture toughness behavior of 10Cr steel at ambient and high temperatures

10Cr steel is one of the candidate materials for turbine rotors of advanced ultra-super critical (AUSC) power plant. Towards characterization of mechanical behaviour of 10Cr steel, the mechanism of plastic flow and fracture behaviour have been investigated in the temperature regime of RT to 600 °C. The flow behaviour (true stress – strain relationship) of the material could be well represented by Voce material model. The tensile properties and work hardening parameters have shown signatures of dynamic strain ageing at intermediate temperatures and dynamic recovery at high temperatures. The fracture behaviour exhibits three distinct regimes of (i) Non-linear elastic fracture behaviour from RT to 250 °C; (ii) Linear elastic fracture behaviour from 300 to 500 °C; (iii) Elastic-Plastic fracture behaviour at 550 & 600 °C. The mechanism of plastic flow and fracture behaviour of 10Cr steel have been discussed in terms of tensile strengths, ductility, work hardening and fracture parameters.

Design of aluminum eco-composite for sustainable engineering application by the valorization of municipal wastes: Experimental and response surface analysis

Reprocessing municipal wastes into useful engineering components is one way to reduce their environmental impact. This paper presents a report on an alternative experimental approach to reprocessing common environmental wastes like aluminum scraps, steel shavings, and coconut shells into eco-friendly engineering composite. Equally, response surface analysis was incorporated in the development and validation of predictive models fit for future prediction of response properties. Aluminum scrap was heated into a liquid state and reinforced with recycled steel particles (RSP) and coconut shell ash particles (CSP) at varying proportions. Specimen design involves three group mixes: A, B, and C. Each of the three groups mixes comprised 0, 1, and 2 % RSP at constant dosage, respectively. Meanwhile, each mix was incorporated with 4, 8, and 12 wt % CSP. The microstructural features, physical (porosity, density, and relative density), and mechanical (tensile strength, hardness, elastic modulus, fracture toughness, impact strength, and percentage ductility) properties were appraised. The outcome revealed that the combination of the two reinforcements (RSP and CSP) contributed to microstructural evolution within the specimens. The porosities of the composite specimens were reported to marginally increase with the reinforcement combination. Interestingly, the composite exhibited lighter weight with improved mechanical performance. Mathematical models derived for the response properties were certified fit for future analysis and predictions. Meanwhile, the optimization procedure revealed that the combination of 1.3 % RSP and 6.7 % CSP was suitable for the design of optimal recycled aluminum composites for sustainable engineering designs. The results clarified that the reinforcement particles (RSP and CSP) are low-cost alternatives to synthetic ceramic reinforcements in the aluminum composite."