Tensile Fracture Mechanism Research Articles

Effect of processing parameters on the microhardness, shear, and tensile properties of layer-cladded Inconel 718

Inconel 718 alloy (IN718) is a popular choice for aerospace hot-end components due to its exceptional mechanical properties. This study investigates the impact of processing parameters (i.e., laser power, powder feeding rate, and scanning speed) on the microhardness, bond strength, and tensile strength of layer-cladded IN718. The results show that IN718 coatings have high microhardness (277.15 HV0.1), strong metallurgical bonding strength (33.97 kN), substantial yield strength (794.09 MPa), impressive ultimate tensile strength (1171.81 MPa), and notable elongation at failure (8.24 %) under laser power is 1.2 kW, powder feeding rate is 250 mg/s, and scanning speed is 4.5 mm/s. In particular, decreased laser energy input enhances microhardness, yield strength, and ultimate tensile strength but reduces bonding strength and elongation. This is attributed to improved Nb element segregation, the reduction of the Laves phase, and grain refinement. However, inadequate energy input leads to cracks and unmelted powder, negatively affecting metallurgical bonding strength. The shear and tensile fracture mechanism of the IN718 coatings is a typical ductile fracture with a microvoid accumulation fracture. The study can facilitate the fabrication of the IN718 coatings with the excellent mechanical properties and the applications in the engineering field.

Hot Tensile Deformation Mechanism and Fracture Behavior of the ZW31/PMMC Laminate

In this work, a Mg-Zn-Y (ZW31) alloy with good plasticity was introduced into 10 μm 10 vol% SiCp/AZ91 composite materials (PMMCs) via the extrusion compound method, and then the ZW31/PMMC laminate was prepared via multi-pass hot rolling. The hot deformation mechanism and elevated temperature tensile fracture mechanism of ZW31/PMMC laminates were studied using the elevated temperature tensile test. The elevated temperature deformation mechanism is influenced by the strain rate. At low strain rates, grain boundary slip is the primary elevated temperature deformation mechanism of the ZW31/PMMC laminate. However, at high strain rates, the activation of pipeline diffusion is facilitated by the particle deformation zone (PDZ) in the PMMC layer with a high dislocation density, leading to the dominance of dislocation climbing as the main mechanism for elevated temperature deformation of the laminate. Additionally, the implementation of a ZW31/PMMC laminate structure effectively inhibits the initiation and propagation of cavities and microcracks within the laminate layer along the normal direction (ND) while simultaneously blunting crack tips via lattice dislocation emission toward the ZW31 layer. Upon cracking of the PMMC layer, stress concentration occurs in the fracture area of the ZW31 layer, ultimately resulting in necking-induced detachment.

Tensile Properties of DD15 Single Crystal Superalloy at Different Temperature

DD15 single crystal nickel-based alloy was prepared by a directional solidification induction heating furnace and its tensile properties were investigated at the 23°C, 400°C, 800 °C, 1100°C and 1140°C. The tensile fracture mechanism of the alloy at different temperature was investigated. Results indicate that tensile strength of the alloy reduces first, increases afterward, and decrease sharply at last as the test temperature rises, while the tensile plasticity exhibit the reverse change trend. The extension strength of the alloy is superior to that of EPM-102 alloy. At 23°C, 400°C and 800°C, the tensile fracture mode of the alloy is quasi-cleavage mechanism, and at 1100°C and 1140°C that is dimple model. As tensile fracture at 23°C, 400°C and 800°C, the γ′ precipitate nearly keeps cube shape, while that becomes rectangular after tensile fracture at 1100°C and 1140°C. The APB and stacking fault can be seen in the γ′ phase at 23°C, 400°C and 800°C. There is dislocation networks at the γ/γ′ interface and the deformation characteristic is dislocation by-passing mechanism at 1100°C and 1140°C.

Strain rate-dependent tensile deformation behavior and fracture mechanism of Mn–N bearing lean duplex stainless steel

The tensile deformation behavior of an Mn–N bearing lean duplex stainless steel (LDSS) with metastable austenite was investigated at the strain rate range of 10−4 - 100 s−1. The mechanical response and microstructural evolution at various strain rate was characterized and in particular, the influence of strain rate on the work hardening, strain-induced martensitic transformation (SIMT) and fracture mechanism was focused on. The results show that the deformation of austenite dominates the overall work hardening and damage mode of the test LDSS. At the strain rate of 10−4 s−1, the test LDSS exhibits excellent strength-ductility combinations with ultimate tensile strength (UTS) of 928 MPa and total elongation (TEL) of 59 %, which are attributed to the occurrence of the SIMT with a typical sequence of γ→ε→α′ and resultant transformation induced plasticity (TRIP) effect. However, the increasing strain rate suppressed the TRIP effect, causing a negative correlation between UTS/TEL and strain rate, because the elevated temperature rise (ΔT) resulting from the adiabatic heating effect promoted increased austenite stability and decelerated SIMT kinetic. Especially at the case of 100 s−1, the higher Ta (average temperature ∼ 23 + 38 = 61 °C), which is close to the Md temperature (the critical temperature up to which martensite formation can be forced by mechanical stress, ∼ 60 °C), leads to a significant increase in stacking fault energy (SFE) within the austenite. Consequently, the microstructural evolution during austenite deformation does not exhibit pronounced SIMT but rather maintains limited twinning. Although the samples deformed at various strain rates exhibit a dimple-type fracture mechanism, the secondary cracking on the fracture faces becomes more pronounced (i.e., reduced fracture resistance) with the decreasing strain rate. Crack initiation frequently appears at the interface of γ/α (or α′/α) for all strain rate cases because of the strain partitioning among constituents, moreover, at lower strain rates (≤10−2 s−1), the cracks inside of the α′-martensite are another damage site, which is responsible for the degradation of fracture resistance.

Synergistic deformation and fracture behavior of heterostructure Cu/1010 steel bimetal laminated composites

In plastic deformation of bimetal laminated composites (BLCs), strength variation, deformation behavior and ductile fracture are quite different from those in single material. The Cu/1010 steel BLCs with different thickness ratio were designed and prepared by continuous solid/liquid bonding. The yield strength (YS), plastic instability strain (PIS) and fracture mechanism were studied by tensile test, mathematical calculations and microstructure characterization. The rule of mixtures (ROM) and long-wavelength approach (LWA) were adopted to study synergistic deformation and the influence factor of PIS combined with the results of finite element method. The deformation behavior and fracture mechanism of the BLCs were analyzed by digital image correlation (DIC) and scanning electron microscopy (SEM). These results demonstrated that, the thickness ratio has a great impact on mechanical behavior of Cu/1010 steel BLCs. In addition to act as a slip barrier to prevent the expansion of the shear band, the interface also increases the YS and flow stress of the BLCs due to its unique strengthening effect. The plastic deformation of Cu/1010 steel BLCs changes from “Cu-dominated” to “1010 steel-dominated” as the volume fraction of Cu decreases, resulting in the decrease in PIS from 25.2% to 12.2%. The PIS calculated by adding accumulated damage to the original LWA was closer to the experimental results, and the maximum error is reduced to about 0.1. The transition of failure mechanism is significantly affected by the strain-hardening and microdefects of the two layers. The current results link the accumulation of microscopic damage to the macroscopic plastic instability, and are of great significance to the understanding of the tensile deformation behavior and fracture mechanism of BLCs.

Investigation of tensile fracture mechanism of Fe-based coatings deposited on different substrates by arc spraying

The adhesion strength of the coating to the substrate determines the service life and performance of components coated by thermal spraying. FeCrMoCBWNb coatings were deposited via arc spraying process to study the adhesion properties of the coatings on Q235 and 65Mn steel substrates. The adhesion properties and tensile fracture mechanisms of the coatings on different substrates were examined by the tensile bonding strength. The phase intensity and crystallinity of the coatings were studied by X-ray diffractometer (XRD). The microstructure and mechanical properties of the coatings were also characterized. The adhesion properties of the coatings depended on the substrates' mechanical properties. The tensile bonding strengths of the coating on Q235 and on 65Mn were 45.5 ± 5.4 MPa and 40.8 ± 1.4 MPa, respectively. The higher substrate roughness of the Q235 steel enhanced the mechanical interlocking of the coating particles to the substrate. The tensile fracture of the coatings comprised brittle and ductile fracture mechanisms.

Tensile properties and fracture mechanism of the Ti2AlC(0001)/TiAl(111) interface: Insights from a first-principles study

A combination of three methods, Griffith theory, work of interface separation, and first-principles tensile simulations, has been applied to uncover the Ti2AlC/TiAl interface's tensile properties and fracture mechanisms. The results show that the three methods give consistent fracture locations when considering the interface elastic energy for work of interface separation, i.e., C-hcp-hollow-BCA fractures inside the TiAl bulk, while Al-fcc-hollow-ACB, Ti(C)-hcp-hollow-ABC, and Ti(Al)-hcp-hollow-BAC all fracture at the interface; Ti(C)-hcp-hollow-ABC has a maximum critical strain (20 %) and the strongest ideal tensile strength (29.32 GPa), because it has a greater deformation energy at the inflection point and it doesn't fracture when Ti(Al)-hcp-hollow-BAC is fully fractured, and the PDOS shape of the interface's Ti atoms exhibits a higher degree of consistency during the tensile process, and the C atoms of the Ti2AlC-2 layer in the Ti(C)-hcp-hollow-ABC exert a strong influence on the Ti atoms at the interface; the fracture mechanism of the Ti2AlC/TiAl interface structure includes the formation of electron holes, the holes increasing, the formation of microcracks, microcracks increasing, the formation of electron depletion region due to a sharp increase in the bond length and the interlayer spacing, followed by a complete fracture.

Investigation of corrosion behavior, tensile and cyclic fracture mechanism of EH36 steel welded joints

This work systematically revealed the static-dynamic corrosion failure behavior of EH36 joints under air, simulated seawater and cathodic protection in seawater. The result indicated that the seawater environment affected tensile performance slightly but acted a critical role in the fatigue behavior. Specifically, the corrosion pit and cyclic stress would respectively induce high-stress concentration and corrosion current density, significantly decreasing the fatigue strength of joints. The application of cathodic protection on joints in seawater would decrease the tensile behavior, but would continuously provide electrons for the surface and crack tip to prevent corrosion damage, improving fatigue performance of EH36 joints.

Controlling anisotropy and brittle-to-ductile transitions by varying extrusion width in short fibre reinforced additive manufacturing

PurposeExtrusion width, the width of printed filaments, affects multiple critical aspects in mechanical properties in material extrusion additive manufacturing: filament geometry, interlayer load-bearing bonded area and fibre orientation for fibre-reinforced composites. However, this study aims to understand the effects of extrusion width on 3D printed composites, which has never been studied systematically.Design/methodology/approachFour polymers with and without short-fibre reinforcement were 3D printed into single-filament-wide specimens. Tensile properties, mechanical anisotropy and fracture mechanisms were evaluated along the direction of extruded filaments (F) and normal to the interlayer bond (Z). Extrusion width, nozzle temperature and layer height were studied separately via single-variable control. The extrusion width was controlled by adjusting polymer flow in the manufacturing procedure (gcode), where optimisation can be achieved with software/structure design as opposed to hardware.FindingsIncreasing extrusion width caused a transition from brittle to ductile fracture, and greatly reduced directional anisotropy for strength and ductility. For all short fibre composites, increasing width led to an increase in strain-at-break and decreased strength and stiffness in the F direction. In the Z direction, increasing width led to increased strength and strain-at-break, and stiffness decreased for less ductile materials but increased for more ductile materials.Originality/valueThe transformable fracture reveals the important role of extrusion width in processing-structure-property correlation. This study reveals a new direction for future research and industrial practice in controlling anisotropy in additive manufacturing. Increasing extrusion width may be the simplest way to reduce anisotropy while improving printing time and quality in additive manufacturing.

Direct tensile mechanical properties and damage fracture mechanisms of thermally damaged coal measures sandstone under high strain rate loading

The direct tensile mechanical properties of highly thermally damaged rock under high strain rate loads are a key basic mechanical problem that must be solved for the stability and effective control of surrounding rock stability in the combustion control area of an underground coal gasification project. In this paper, a two-dimensional equivalent grain-based model (GBM) unit and Split Hopkinson Tension Bar (SHTB) numerical model for thermally damaged coal-measures sandstone were constructed using particle flow code (PFC). The comparison with the experimental results shows that the numerical method can accurately describe the dynamic direct tensile behavior of thermally damaged sandstone. The following conclusions are drawn: The dynamic tensile strength of thermally damaged sandstone shows a significant strain rate-strengthening effect. With the increase in thermal damage temperature, the dynamic tensile strength of sandstone increases first and then decreases. The generation and development of hot cracks in a high-temperature environment is the fundamental reason for the change in macroscopic mechanical properties. The dynamic tensile failure process of thermally damaged sandstone can be divided into four stages: the dynamic damage initiation, the dynamic damage development, the damage crack penetration, and the sample dynamic fracture. With the increase in impact velocity, the initial kinetic energy, elastic strain energy, dissipated energy, and elastic strain energy ratio in the failure process of thermally damaged sandstone gradually increase. In contrast, the dissipated energy ratio gradually decreases. As the heat treatment temperature increases, the elastic strain energy and the ratio of elastic strain energy increase first and then decrease.

Tensile behaviors of nanoporous phenolic composites reinforced by 3D needle-punched preforms with different weave patterns

Needle-punched preform reinforced nanoporous phenolic composite (NPC) is a cost-effective lightweight ablative material for thermal protection systems. It consists of a needle-punched preform composed of alternating stacked fiber felt and stacked woven fabric, which plays a crucial role in the thermal insulation efficiency and mechanical properties. Herein, needle-punched preforms with different types of fabrics, including plain, twill, and satin, are deliberately designed for the reinforcement of NPC, and their tensile properties and fracture mechanism are investigated through experimentation and the CT image-based finite element method. At the same preform density, the composite with plain fabric exhibits the highest tensile strength of 146 ± 6.3 MPa, a tensile modulus of 8.2 ± 0.2 GPa, and an elongation of 2.1 ± 0.1%, due to having the highest number of crossover points and the largest undulation of fiber yarns. Furthermore, the CT image-based simulation reveals the failure mechanism of NPC. The von mises stress of woven fabric is higher than that of fiber felt, which demonstrates the woven fabric is the main load-bearing structure and determines the mechanical of composite. These results will provide useful guidance for the structural design and optimization of needle-punched preform reinforced composites.

Comparative study on microstructure and mechanical properties of a novel nano-composite strengthening heat-resistant steel and two typical heat-resistant steels

In this study, a new nano-composite strengthening austenitic heat-resistant steel designed for ultra-super critical (USC) thermal power plants was analyzed in comparison with the traditional H3RC and S30432 heat-resistant steels to assess its reliability. The microstructure, precipitates, hardness, tensile property and low cycle fatigue behaviors of the three steels at room temperature and service temperature were characterized. The results show that the SP2215 has finer grains, higher twin density, more primary MX, NbCrN and M23C6 precipitates compared with the HR3C and S30432 steels. The main precipitates in the steels after solution treatment are secondary (Nb, V)(C, N) phase (MX). The subsequent aging treatment of the SP2215 steel results in precipitation of the M23C6 carbides at the grain boundaries and Cu-rich phase inside the grains. As a result, the SP2215 steel shows higher Vickers hardness, tensile and fatigue strength (400 MPa) at room temperature than the other two steels. Transgranular fracture is the dominant tensile fracture mechanism of the three steels at room temperature, while intergranular cracking becomes the main fracture mode at high temperature due to precipitation of the continuous M23C6 at the grain boundaries. At the temperature of 700 ºC, fatigue strength of the SP2215 under a peak stress lower than 450 MPa decreases only a little.

Tensile and long-term creep properties of structurally and functionally integrated carbon fiber reinforced plastic at room temperature

Carbon fiber reinforced plastic (CFRP) based on phenolic resin have been widely used in aerospace and pressure vessel fields because of their high stiffness to weight ratio and excellent mechanical properties. In this paper, carbon fiber reinforced plastic were prepared by molding method using phenolic resin as the matrix. The fiber distribution inside the material and its influence on tensile fracture mechanism and creep properties were investigated. The specimens were prepared along horizontal and vertical directions. The test results show that the fibers tend to be distributed horizontally within the material and are influenced by the mold. Horizontal specimens with a large number of fibers parallel to the tensile direction exhibit more excellent tensile properties. The vertical specimen is loaded by the resin and interface with weaker properties inside. The fracture mechanism of horizontal specimens is fiber breakage, fiber pullout and resin fracture, while the fracture mechanism of vertical specimens is interfacial debonding and resin fracture. The difference in tensile fracture mechanism of horizontal and vertical specimens affects the creep properties of CFRP. The creep resistance of fiber is better than that of resin. Therefore, horizontal specimens exhibit better creep resistance in long-term creep tests due to the loads borne by the fibers. Modified Time Hardening model can accurately fit all experimental data. Creep curves can be predicted based on the model parameters.

Effect of infill density and reinforced perimeters on tensile properties and fracture mechanism of 3D printing carbon fiber–reinforced composite

Effect of infill density and reinforced perimeters on tensile properties and fracture mechanism of 3D printing carbon fiber–reinforced composite

Effects of uniaxial stress and temperature on the interfacial tensile strength and stability of Al/NiO nanolaminates: A first-principles study

Nanoenergetic multilayer films have been widely prepared due to their unique advantages in realizing “nanoenergetics-on-a-chip”. Recently, the potential for adjusting the performance of nanothermites without altering their film thickness has attracted much attention, prompting researchers to concentrate on film stress. Here, we employed first-principles tensile tests and ab initio molecular dynamics simulations to investigate the tensile properties, fracture mechanisms, and film stability of two Al/NiO interfaces under pre-stress. An analysis of electron localization function and bond overlap population shows that the weakest locations of the (100)-Top and (111)-Top interface systems are distinctly different, leading to two different fracture mechanisms. When the pre-stress and temperature are coupled, the reactivity of Al/NiO as an energetic material is enhanced. Particularly for (111)-Top, the amorphous, mixed region between the two phases replaces the original coherent interface. With the increase of the pre-stress, the crack evolves ahead of the critical strain, indicating that the coupling effects of the pre-stress and temperature have an important influence on the stability and fracture strength. This work not only reveals the mechanical properties of Al/NiO, but also provides a theoretical guidance for optimizing the structure of energetic nanolaminates.

Experimental study on the dynamic tensile failure of bamboo

Bamboo is a fast-growing biomaterial with excellent mechanical properties, which can be used for different applications, such as bridges and automobiles. This study employed the split Hopkinson tensile bar (SHTB) tests with the strain rate changed from 600 s−1 to 1200 s−1 and quasi-static tensile tests to investigate the dynamic tensile failure of Moso bamboo material systematically. Specimens’ mechanical properties, stress–strain responses, and tensile failure mechanism were discussed. Results showed that the tensile performance of both internode and node specimens improved with increasing strain rate. The dynamic increase factor (DIF) of node specimens was more significant than that of internode specimens. The fibers pulling out, interlocking effect and slippage failure are important failure mechanisms of brittle-ductile transition. The crack deflection, fibers pulling out, interlocking effect, synergistic deformation and slippage can be considered critical toughening mechanisms. This study fills the knowledge gaps between strain rate and dynamic tensile fracture mechanisms of bamboo material and provides a reference for dynamic engineering applications of bamboo.

A Micromechanics-Based Model of Direct Tensile Fracture in Brittle Rocks under Confining Pressure

A novel micromechanics-based model in brittle rocks is presented during the confined tensile fracture. This model is formulated by using the stress intensity factor of crack under distinct loading modes in the fracture mechanics theory. The confined tensile fracture mechanisms with and without initial crack friction are established. The development process from the confined tensile fracture without initial crack friction to that with initial crack friction is studied. The stress–strain constitutive relationship describing the transformation mechanism from the unloading of axial stress at a compressive state to the loading of axial stress at a tensile state is also studied during the confined tensile fracture. The tension–compression transformation mechanism codetermined by the friction of the initial crack, the angle of initial crack inclination, and the confining pressure is proven. With the decrease of the angle of initial crack inclination or the increase of the confining pressure, the confined tensile fracture constitutive model tends to be dominated by the tensile fracture mechanism with initial crack friction. The confined tensile fracture of brittle rocks tends to happen at the larger angle of initial crack inclination. The reasonableness of the presented model is checked by contrasting the experimental data. Effects of the friction, density, inclination angle and size of the initial crack, and the confining pressure on the tensile relation curve of strain and stress, the tensile relation curve of crack length and stress, the tensile elastic modulus, the tensile stress of crack initiation, and the tensile strength are discussed.

Structure and tensile fracture mechanism of aluminum matrix composites produced by internal oxidation

This article presents experimental results of resistance against fracture upon static tension of cast aluminum matrix composites based on aluminum with various content of Al2O3 strengthening phase. The cast aluminum matrix composite materials were produced by the technology based on burnout of aluminum melt upon interaction with oxygen. Two batches of ingots with various content of solid phase were smelted for tests of static strength. The average particle size of strengthening phase of predominantly prismatic morphology was 60–80 μm, and their content varied from 15 to 25 %. The fracture surfaces obtained upon static uniaxial tension of the considered samples were studied on the samples destroyed at maximum stress. The fracture surfaces were analyzed using an optical microscope with expanded options due to improved long-focus system and digital processing of images based on unique procedure of 3D structure analysis. For indepth analysis of characteristic fracture region a scanning electron microscope was used equipped with energy and wavelength dispersive elemental analyzers. It was established in the studies that in the samples with lower content of dispersed phase, the fracture is characterized by mixed heterogeneous in terms of macrogeometry pattern. This can be interpreted as dry fibrous fracture with visible crystalline pimples and breakaways. With an increase in the solid phase, a mixed, sufficiently homogenous in terms of macrogeometry, fracture pattern of fanlike fibrous structure can be observed. Crystalline pimples were also detected of a different fracture surface area, as well as breakaways of other geometrical sizes. The features of changes in the relief of fracture surface and the fracture mechanisms of the obtained composites have been detected and described.

Effect of grain size on the tensile ductility and fracture mechanism of Ti–O alloys

Several recent studies reported high ductility in the Ti–O alloy, which is believed to be brittle, but the mechanism explaining the ductility has not yet been clarified. This study focused on the relationship between grain size and ductility to elucidate the mechanism for the high ductility in the Ti–O alloy and found that the ductility decreased with an increasing grain size. Although the extrudate of a Ti-0.77 wt%O sintered alloy exhibited good ductility (>5%) up to a grain size of 49.8 μm, the alloy failed in the elastic area when the grain size exceeded 98.4 μm. Cracks with a size similar to the grain size were observed at the grain boundaries in the fracture area of these ductile fine-grain Ti–O alloys. In situ observations of the deformation behavior of the fine-grain Ti–O alloy revealed that crack propagation was suppressed due to the reduced stress intensity caused by crack refinement. In contrast, in the large-grain Ti–O alloy, the high stress intensity around the first crack caused immediate crack propagation and brittleness.

Temperature and Strain Rate Dependence on the Tensile Mechanical Properties, Constitutive Equations, and Fracture Mechanisms of MarBN Steel.

The effect of strain rate and temperature on the thermomechanical behavior and microstructure of MarBN steel is studied with the strain rates of 5 × 10-3 and 5 × 10-5 s-1 from room temperature (RT) to 630 °C. At high strain rates of 5 × 10-3 s-1, the Holloman and Ludwigson equations can better predict tensile plastic properties. In contrast, under low strain rates of 5 × 10-5 s-1, coupling of the Voce and Ludwigson equations appears to predict the flow relationship at RT, 430, and 630 °C. However, the deformation microstructures have the same evolution behavior under strain rates and temperatures. Geometrically necessary dislocations appear along the grain boundaries and increase the dislocation density, which results in the formation of the low-angle grain boundaries and a decrease in the number of twinning. The strengthening sources of MarBN steel include grain boundary strengthening, dislocation interactions, and multiplication. The fitted R2 values of these models (JC, KHL, PB, VA, ZA) to plastic flow stress at 5 × 10-5 s-1 are greater than 5 × 10-3 s-1 for MarBN steel. Due to the flexibility and minimum fitting parameters, the phenomenological models of JC (RT and 430 °C) and KHL (630 °C) give the best prediction accuracy under both strain rates.