Tensile Fracture Mechanism Research Articles

In-situ investigation on dislocation slip concentrated fracture mechanism of linear friction welded dissimilar Ti17(α+β)/Ti17(β) titanium alloy joint

In this research, the tensile deformation behavior and fracture mechanism of linear friction welded dissimilar Ti17 (α+β)/Ti17(β) titanium alloy joint were investigated in-depth by in-situ tensile test performed under scanning electron microscopy and further microstructural characterizations using electron backscatter diffraction technique and transmission electron microscopy. The results show that dislocation slip is the dominant deformation behavior of the joint during tensile loading, which occurs in the metastable β matrix and can be impeded by α phase. This effect is concentrating on the Ti17(β) side thermo-mechanically affected zone (TMAZ-(β)), and close to Ti17(β) side heat-affected zone (HAZ-(β)), where a large amount of α is dissolved and transformed into metastable β. The crack initiates from this area owing to microvoids coalescence and propagates along the slip line until fracture. In the other areas of the joint, the relatively high content of α phase, fine grain strengthening caused by dynamic recrystallization, and strain strengthening produced by microstructure deformation, all significantly reduce dislocation slip and hinder crack initiation. Therefore, the fracture mechanism can be attributed to concentration of dislocation slip in TMAZ-(β) close to HAZ-(β), which also results in the tensile strength and elongation of the joint were 1062.1 MPa and 3.5%, respectively, lower than those of the two base metals.

Effect of subsurface damage on tensile behavior and fracture mechanism of SiCp/Al composites: Experimental analysis and RVE modeling

Machining-induced subsurface damage (SSD) is crucial for the reliable application of composite components. This paper investigated the SSD characteristics and its effect mechanism on tensile behavior and fracture mechanism for SiCp/Al/45%p based on experimental analysis and numerical modeling. Specifically, a representative volume element (RVE) model considering SSD was established to reveal the crack initiation and propagation in uniaxial tension. The digital image correlation (DIC) technique was used for monitoring the tensile strength and full-field strain of specimens containing SSD. The results showed that the increase in SSD depth decreases the tensile strength, which declined by 16.3% from 258 MPa to 216 MPa when SSD depth increased from 60 μm to 210 μm. The εxx maximum negative strain in the high-stress state and the εyy maximum positive strain in the low-stress state were susceptible to increased SSD depth. The fractography characteristics analysis showed the initial fracture position of the specimens was within the SSD area. The brittle fracture of particles and ductile fracture of the matrix are the main fracture mechanisms of SiCp/Al/45%p. A few particle-matrix interface failure was observed. Moreover, the RVE model indicates that the location of particle fracture and particle debonding damage is prone to generate stress concentrations, leading to crack initiation and propagation. This study provides a new sight and theoretical guidance for the reliability application SiCp/Al composite.

Molecular dynamics investigation of the mechanical properties and fracture behaviour of hydroxyl-functionalised carbon and silicon carbide nanotubes-reinforced polymer nanocomposites

ABSTRACT The tensile properties and fracture mechanism of hydroxyl-functionalized silicon carbide nanotubes (O-fSiCNTs) inserted into polymer matrices are explored and the outcomes are compared to results for the hydroxyl-functionalized carbon nanotubes (O-fCNTs) incorporated in similar matrices. The molecular dynamics (MD) method is used and the simulations are based on the notion of representative volume elements (RVEs). The incorporation of chemisorbed nanotubes in polymers has a profound effect on the enhancement of their mechanical properties. The O-fSiCNTs inside the polyethylene (PE) and polypropylene (PP) (O-fSiCNTs/PE and O-fSiCNTs/PP) possess lower Young’s modulus, maximum stress, and strain energy as compared to the O-fCNTs/PE and O-fCNTs/PP. The zigzag O-fSiCNTs/polymer experiences lower bearable maximum strains in response to imposed loads in comparison with the O-fCNTs/polymer which is opposite to what occurs in the armchair O-fSiCNTs and O-fCNTs/polymer. The more the functionalization degree is, the weaker the structure is and its stiffness, tensile strength, tolerable strain before fracture, and ability to absorption of internal energy decline. Not only are the zigzag O-fSiCNTs/polymer stiffer than the armchair O-fSiCNTs/polymer in every percent of functionalization, but also as compared to the armchair ones, they show a lower decrease in the variation of Young’s modulus with increasing the functionalization percentage.

Exceptional fatigue resistant NiTi wire mediated by R-phase

Ni50.2Ti49.8 and Ni50.9Ti49.1 wires in cold-drawn state were compared regarding tensile fatigue life and fatigue fracture mechanism. Through process control, Ni50.2Ti49.8 with R-phase matrix at room temperature was achieved in as-drawn state without post heat treatment. The R-phase imparts exceptional fatigue performance to Ni50.2Ti49.8 wire with fatigue life approximately twelve times of that for Ni50.9Ti49.1 which comprises B2 phase and a small amount of B19′ under the same test conditions. The cyclic phase transformation under loading initiates microcracks in phase boundaries, leading to premature fracture of Ni50.9Ti49.1. In contrast, the R-phase presents exceptional stability against fatigue failure upon cyclic loading.

Tensile Properties and Fracture Mechanism of Thermal Spraying Polyurea.

In this study, polyurea was experimentally tested under various spraying temperatures and pressures. The number of holes and the pore size produced after the tensile fracture of the polyurea were counted to illustrate the effect of the various spraying temperatures and pressures on the performance of the polyurea. The tensile characteristics of polyurea were greatly influenced by the spraying temperatures and pressures, according to the experimental findings and statistical analysis. The polyurea tensile performance was best when the spraying pressure was 17.25 MPa with a spraying temperature of 70 °C. The fracture mechanism was illustrated by the silver streaking phenomenon generated during the tensile stretching process. The fracture energy was absorbed by the fracture holes and pores during silver streaking, thus creating the huge gap in tensile properties.

Influence of the heating force in rotational friction welding on mechanical properties and tensile fracture mechanism of dissimilar welded joints of 30KhGSA and 40KhMFA steels

This article presents the results of evaluating the effect of heating force, as one of the parameters of rotational friction welding, on the mechanical properties and mechanism of tensile failure of dissimilar welded joints of medium-carbon steels 30KhGSA and 40KhMFA. The results of studies of the microstructure and microhardness of welded joints are presented. The fracture mechanism of welded specimens during tensile testing was evaluated on the basis of strain distribution maps obtained by the digital image correlation method and the results of fractographic analysis. The features of the development of deformation and failure of welded joints obtained at different heating forces are shown. From the point of view of the equal strength of the structure with a welded joint the optimal values of this parameter of rotary friction welding for joining steels 30KhGSA and 40KhMFA are recommended.The reported study was funded by RFBR according to the research project № 20-38-90032.When conducting mechanical tensile tests and studying the distribution of deformation fields, equipment was used that is part of the Plastometriya collective centre of the IES named after E. S. Gorkunova of the Ural branch of the RAS

Effects of Moisture and Synthesis-Derived Contaminants on the Mechanical Properties of Graphene Oxide: A Molecular Dynamics Investigation.

This paper reports on the effects of the chemical composition of graphene oxide (GO) sheets on the mechanical properties of bulk GO. Three key factors were analyzed: (i) the oxygenated functional groups' concentration, (ii) the content of intersheet water (moisture), and (iii) the presence of residual contaminants observed from the synthesis of GO. Molecular dynamics simulations using the reactive force field ReaxFF were conducted to model tensile strength, indentation, and shear stress tests. The structural integrity of the carbon basal plane was the primary variable that determined mechanical behavior of GO slabs. Hydrogen-bond networks played an essential role in the tensile fracture mechanism, delaying the onset of fracture whenever strong hydrogen bonds existed in the intersheet space. The presence of interlayer sulfate ion contaminants negatively impacted the tensile strength, stiffness, and toughness of GO. Moreover, it was observed that intersheet sulfate ions improved the resistance to fracture of GO at low sulfur concentrations, while lower fracture strains were observed beyond a critical concentration. Alike the tensile stress findings, the indentation properties were determined by the integrity of the carbon basal plane. Our findings agree with experimental mechanical property measurements and reveal the importance of considering synthesis-derived contaminants in molecular models of GO.

Effect of samarium modification on the microstructures evolution and mechanical properties of high strength aluminum alloy

High strength aluminum alloys have been used in various industries, but increasing the strength and ductility of the alloy simultaneously remains a challenge. To solve this problem, a novel Al-Zn-Mg-Cu-Zr( Sm) alloy with Sm addition was prepared. The results show that the Sm element exists in the form of Al 10 Cu 7 Sm 2 phase, with a small amount distributed in the matrix and eutectic phases. After Sm modification, the recrystallization behavior was inhibited, and the substructure and deformation microstructure in the extruded alloy were improved. Moreover, Sm can effectively promote the formation of η’ phase and inhibit the conversion of η’ phase to η phase. Based on the above factors, the strength of the alloy was improved. Meanwhile, for the modified alloy, grain refinement reduces crack nucleation and finely dispersed precipitates reduce stress concentration, which is also responsible for the increased ductility of the alloy. • The effect of different Sm content on the microstructure of Al-Zn-Mg-Cu-Zr alloy was studied. • Sm in Al-Zn-Mg-Cu-Zr alloy mainly exists as Al 10 Cu 7 Sm 2 intermetallic compound, and a small amount is dissolved in the matrix and eutectic phase. • Sm can inhibit the recrystallization behavior of the alloy and promote the precipitation of η’ phase. • When the Sm content is 0.3%, the alloy has higher strength and toughness. • Mechanism of tensile fracture and alloy strength and toughness improvement is discussed.

Superior High‐Temperature Properties of Low‐Density Steel Enabled by a Tunable Hierarchical Microstructure

The tensile properties, microstructure characteristics, and fracture mechanisms at 500 °C of Fe–Mn–Al–C–Mo–V steel processed by hot rolling (HR) and warm rolling (WR) are investigated. The HR steel obtained by rolling 1150 °C, consisting mainly of equiaxed austenite and banded ferrite, exhibits a tensile strength of 695 MPa, accompanied by an elongation of ≈45.5%. In contrast, the WR steel processed by rolling at 750 °C shows a hierarchical microstructure that consists mainly of lamellar ferrite/austenite + fine carbides, rendering a significantly increased tensile strength to 1040 MPa and an excellent elongation to ≈20.0%. This is mainly attributed to the remarkable refinement of ferrite and austenite in the WR steel, strengthening finely dispersed carbides, and obtaining numerous low‐angle grain boundaries in the matrix. The tensile fracture morphology is a ductile failure in both types of steel. The fracture of HR steel is attributed to the cracks enabled by the austenite localized slip deformation in the austenite and the fracture of the precipitates; the failure of the WR steel is mainly ascribed to the cracking along the lamellar structure due to the κ‐carbides pinning lamellar ferrite phase boundary leading to high strain localization.

Interface structure and tensile behavior of high entropy alloy particles reinforced Al matrix composites by spark plasma sintering

Aluminum matrix composites (AMCs) reinforced with AlCoCrFeNi high entropy alloy (HEA) particles were fabricated by spark plasma sintering (SPS). The interface formation between the HEA particles and Al matrix, tensile properties and fracture behavior were investigated. The interface has a two-layer structure, the interface reaction layer close to the HEA particles was Al13(CoCrFeNi)4, and the interface reaction layer near the Al matrix was composed of Al9(CoFeNi)2 and Al18Cr2Mg3. The addition of HEA particles increased the yield strength, and reduced tensile strength and elongation of the composites. The fracture occurred at the interface reaction layer near the HEA particles, exhibiting obvious brittle fracture feature. The tensile fracture mechanism of the SPSed HEA/Al AMCs can be attributed to the poor plastic deformation ability of continuously distributed Al13(CoCrFeNi)4 and aggravated degree of stress concentration at interface reaction layer close to the HEA particles.

Correlation between corrosion behavior and grain boundary characteristics of a 6061 Al alloy by lab-scale X-ray diffraction contrast tomography (DCT)

In this work, the corrosion behavior of a peak aged 6061 Al alloy was investigated through a combination of x-ray tomography and lab-scale x-ray diffraction contrast tomography (DCT). Pitting corrosion and intergranular corrosion (IGC) were both observed when the alloy was immersed in a 3.5 wt% NaCl solution. Pitting corrosion happens at the position of both Al 5 FeSi inclusions and Mg 2 Si precipitates. The intergranular corrosion is actually caused by the galvanic cell between grain boundary precipitates and the matrix. The 3D distribution of grain boundary characteristics was quantitatively analyzed by DCT and correlated with the IGC behavior. Investigations revealed that grain boundaries with misorientation angles smaller than 25° or larger than 45° exhibited stronger resistance to IGC. Grain boundaries with misorientation between 25° and 45° corroded more easily. The influences of IGC on the tensile properties and fracture mechanisms were also elucidated in this work. • The corrosion behavior of 6061 Al alloy was investigated by x-ray tomography and diffraction contrast tomography (DCT). • The pitting corrosion related with the Al 5 FeSi inclusions was revealed. • The correlation between intergranular corrosion and grain boundary characteristics was revealed.

Mechanical properties of 2D Zr n +1C n (n = 1, 2) MXenes with and without functionalization

Transition metal carbides and nitrides (MXenes) are considered the new generation of flexible electronic materials because of their superior mechanical strength and flexibility. Based on the density functional theory, the structures, electronic properties and mechanical properties of the 2D Zr-based MXenes with and without surface functional groups (O, F and OH) are investigated systematically to explore their elastic properties and tensile fracture mechanism. The results reveal the tensile strength and critical strain under biaxial tensile direction can reach 52 GPa, 12% for Zr2C and 55 GPa, 19% for Zr3C2, more outstanding than the mechanical behavior of the pristine Ti2C (47 GPa, 9.5%). The tensile behaviors of the functionalized Zr n +1CnT2 (n = 1, 2, T = O, F, OH) strongly depend on the crystallographic orientation and the surface functional group. The phonon spectrum under the critical strain indicates the tensile fracture of the pristine Zr-based MXenes was determined by phonon instability, except along the armchair direction of Zr2C and zigzag direction of Zr3C2. During tensile strain, the collapse of Zr n +1C n F2 and Zr n +1C n (OH)2 (n = 1, 2) are mainly caused by internal Zr–C bond rupture and transfer to the surface. While the O-functionalized Zr n +1C n O2 (n = 1, 2) presented the opposite collapse trend. Additionally, according to the research results of critical strain, elastic modulus and electrical conductivity, F/OH-terminated Zr2C MXene is relatively more suitable for flexible sensors of wearable devices than Zr3C2T2.

Mechanical properties of welded ultrahigh-strength S960 steel at low and elevated temperatures

New ultrahigh-strength steels have been developed to meet the need for better performance, load bearing capacity, safety and weight saving. However, the design guidelines are incomplete, especially regarding the design of welded ultrahigh-strength steel components in fluctuating operating conditions. This reduces usability and can cause serious safety risks when the welded structures are in use. The heat input and cooling rate have a significant effect on the microstructure and mechanical properties of the ultrahigh-strength steels. Therefore, a model to predict the strength and microstructure, based on welding parameters, is required for designers to create safer solutions in engineering design. In this study, a 6 mm thick S960 low alloy ultrahigh-strength steel was welded using gas metal arc welding (MAG) and laser welding. The effects of welding heat input and operating temperature on the tensile properties, hardness, microstructure, and fracture mechanism of the welded specimens were investigated. The effects of operating temperature on the mechanical properties of welded joints were investigated by performing tensile tests between temperatures of −80 °C and + 400 °C. The unwelded base material was also tested in the same temperature range. The results showed a ductile fracture mechanism in all the samples regardless of the test temperature and welding heat input. However, the tensile strengths and elongations increased when the test temperature drops to −80 °C from room temperature. In addition, mathematical predictions for the strength and elongation properties, and grain sizes in heat-affected zones, as a function of temperature and welding heat input were proposed.

Microstructure and its effect on high temperature tensile properties of T92/HR3C dissimilar weld joints

A T92/HR3C dissimilar metal weld joint, which is widely used in the boiler components of ultra-supercritical power plants, was fabricated by manual tungsten inert gas welding with Inconel 82 as the filler metal. This study reports the high-temperature tensile properties, deformation behavior, and fracture mechanism of dissimilar weld joints. The results of tensile tests at 640 °C show a severe strength mismatch between the weld metal and the heat-affected zone of the T92 steel (T92-HAZ). The serrated flow behavior of the T92/HR3C weld joint at different tensile rates was observed during plastic deformation. Based on the results of transmission electron microscopy, dynamic recrystallization and re-precipitation of Cr23C6 carbides both likely triggered the serrated flow behavior and enhanced the tensile strength of the weld metal. Additionally, the inter-critical T92-HAZ was the weakest zone in the weld joint because of the dissolution of a large amount of carbides and the transformation of martensite laths into equiaxed subgrains.

Atomistic simulation and continuum modeling of the dynamic tensile fracture and damage evolution of solid single crystalline Al with He bubble

The dynamic tensile fracture mechanism and damage evolution characteristics of solid single crystalline Al with He bubble are investigated by molecular dynamics (MD) simulations and continuum modeling. The physical mechanism leading to fracture is found to be dominated by He bubble growth, in wide ranges of strain rate and initial bubble volume fraction. The bubble growth process can be divided into three stages and the microscopic mechanism is related to the plastic deformation of surrounding metallic material predominated by dislocation growth and movement. It is further revealed that the evolution characteristics of He bubble are independent on strain rate or initial bubble volume fraction, but the growth rate increases significantly with increasing strain rate or decreasing bubble fraction. Additionally, the critical stress for bubble growth and dynamic tensile strength at the strain rates from 106 /s to 1010 /s are obtained, showing strain rate hardening effect. Finally, a continuum model based on the understanding derived from MD simulations is proposed to describe the damage evolution of the metal with He bubble, including the new strength softening effect induced by bubble growth. The dynamic tensile processes at the strain rates from 104 /s to 1010 /s are calculated by this model, and the obtained pressure and bubble evolutions and dynamic tensile strength are in good agreement with available MD results. We suppose that the present study sheds some light on the dynamic fracture of solid metals containing He bubble.

Microstructure inducement of different tensile fracture mechanisms at 800 ℃ of directional solidified Ti-45Al-5Nb alloys produced by electromagnetic confinement

Directional solidified TiAl alloys have low density and good comprehensive high temperature performance, which is an ideal substitute material for high temperature structural parts. In this paper, Φ 16.5 mm directional solidified Ti-45Al-5Nb sample with full-lamellar microstructure was prepared successfully by electromagnetic confinement technique at 10 µm/s and relative tensile tests at 800 ℃ were also performed. The tensile strength of Ti-45Al-5Nb alloy at 800 ℃ is 765 MPa and the elongation is 16%. Moreover, results of tensile process characteristics and fracture analysis show that this material has two distinct fracture mechanisms at 800 ℃, which are cleavage fracture mechanism and microporous aggregation fracture mechanism. Two fracture mechanisms do not exist at the same time, and for a particular specimen, the fracture process is dominated by only one of them. Different fracture mechanisms are determined by the lamellar orientation difference and element segregation. When the orientation of adjacent grains is similar and the segregation is light, the fracture process is dominated by the cleavage fracture mechanism. Otherwise, proportion and scale of the γ phase at the grain boundary increase and the B2 phase is generated. In this case, the microporous aggregation fracture mechanism will dominate the fracture process.

Solidification characteristics and high temperature tensile properties of Ni-based superalloy IN713C

The solidification characteristics and high temperature tensile properties of IN713C superalloy were investigated using directional solidification methods at withdrawal rates of 10, 50 and 100 µm/s, respectively. The results show that carbide morphologies change from block and long strip to short rod and granular with increasing withdrawal rate. The increase of withdrawal rate promotes the microsegregation of Mo, Nb and Zr, and contributes to precipitation of the γ/γ’ eutectic and boride. With the withdrawal rate increasing from 10 µm/s to 50 µm/s, the high temperature yield strength, ultimate strength and elongation of the IN713C alloy increased by 11.8%, 18.3% and 64% respectively. The increase of the γ/γ’ eutectic and boride lead to slight decrease in strength when the withdrawal rate increased from 50 µm/s to 100 µm/s. The fractographic observation of tensile specimen indicates that the integrate carbide particles are an overwhelming majority at a higher withdrawal rate. When the withdrawal rate decreases, the particles become larger and more secondary cracks are generated. The morphology of carbides affects the tensile fracture mechanism of the alloy. With the decrease of carbide size, the crack source of the IN713C alloy changed from brittle carbides to the interface between carbide and matrix.

Revealing the influence of ultrasound/heat treatment on microstructure evolution and tensile failure behavior in 3D-printing of Inconel 718

Ultrasound is a potential method to enhance the mechanical properties during directed energy deposition (DED), however, its intrinsic strengthening mechanism has not been completely uncovered. In this study, the ultrasound-induced strengthening mechanism has been explored from perspectives of microstructure evolution (i.e., grain size and phase composition), and it has been compared with that of the heat treatment after building without ultrasound. The results indicate that the columnar grain (γ) underwent obvious transition and refinement by inducing ultrasound, along with the changes in the morphology and size of Laves phase. Yet the second phase (i.e., γ′ + γ″, Laves phase, and δ) of heat-treated samples was different than that of the samples obtained by ultrasound. Moreover, combined with grains changes and the quantitative analysis of Laves phase, the tensile properties and fracture mechanism were analyzed. The experimental results demonstrate that the tensile properties were improved by both ultrasound and heat treatment. Among them, the average ultimate tensile stress of samples treated with ultrasound increased by 10% compared to the as-built samples along the scanning direction. Consequently, the main strengthening mechanism of samples by ultrasound was found to be grain refinement, while a large number of strengthening phases (γ′ + γ″) precipitated to strengthen the matrix in heat-treated samples. Thus, clarifying strengthening mechanism is crucial for understanding the mechanical properties of as-built samples.

Initial Microstructure Effects on Hot Tensile Deformation and Fracture Mechanisms of Ti-5Al-5Mo-5V-1Cr-1Fe Alloy Using In Situ Observation

The hot tensile deformation and fracture mechanisms of a Ti-5Al-5Mo-5V-1Cr-1Fe alloy with bimodal and lamellar microstructures were investigated by in situ tensile tests under scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the main slip deformation modes are prismatic slip ({11¯00}<112¯0>) and pyramidal slip ({11¯01}<112¯0>) under tension at 350 °C. In the bimodal microstructure, several parallel slip bands (SBs) first form within the primary α (αP) phase. As the strain increases, the number of SBs in the αP phase increases significantly and multislip systems are activated to help further coordinate the increasing deformation. Consequently, the microcracks nucleate and generally propagate along the SBs in the αP phase. The direction of propagation of the cracks deflects significantly when it crosses the αP/β interface, resulting in a tortuous crack path. In the lamellar microstructure, many dislocations pile up at the coarse-lath α (αL) phase near the grain boundaries (GBs) due to the strong fencing effect thereof. As a result, SBs develop first; then, microcracks nucleate at the αL phase boundary. During propagation, the cracks tend to propagate along the GB and thus lead to the intergranular fracture of the lamellar microstructure.

Influence of Morphology Characteristics on Shear Mechanical Properties of Sawtooth Joints

The interface problem exists widely in building. Joints are interfaces of rock mass structures. To further study the influence of morphological characteristics on the shear mechanical properties of sawtooth joints, this paper prepared rock-like materials based on the similarity principle and carried out direct shear tests of sawtooth joints. The results showed that: (1) the peak shear displacement of joints first increases and then decreases with increasing normal stress, but the normal trend of stress during turning is different under different sawtooth angles. When the sawtooth angle of the joints is small, the decrease in shear stress between shear strength and residual shear strength is not obvious, and the rate of decrease is also small. (2) The shear strength of joints is positively correlated with normal stress. Using the Mohr–Coulomb criterion to analyze the shear strength of joints, it was found that the cohesion c and internal friction angle α of joints increased nonlinearly with increasing sawtooth angle, but their increasing trends were different. By introducing the function relation between cohesion, internal friction angle, and sawtooth angle into the classical shear strength equation, an empirical equation for the shear strength of joints was established in consideration of sawtooth angle. (3) There are two modes of shear failure for serrated joints: the “saw-toothed sliding gnawing failure mechanism” (SSG) and the “tensile fracture mechanism” (TFM). In the SSG, the shear failure mode of joints evolves in a slipping–gnawing–complete gnawing mechanism with increasing sawtooth angle and normal stress. The TFM mainly occurs at high sawtooth angles. This study provides a theoretical reference for the prediction and prevention of geological disasters.