Tensile Failure Mechanisms Research Articles

Experimental Investigation on the Mechanical and Dynamic Thermomechanical Properties of Polyether Ether Ketone Based on Fused Deposition Modeling.

In this work, the mechanical and dynamic thermomechanical properties of PEEK based on FDM are experimentally investigated and evaluated comprehensively. The tensile failure mechanism of PEEK prepared by FDM and extrusion modeling (EM) was analyzed by fracture morphology observation. By conducting a differential scanning calorimetry (DSC) test, the crystallinity of PEEK prepared by FDM and EM was measured. The dynamic thermomechanical properties of PEEK were tested and analyzed by dynamic mechanical analysis (DMA). For FDM-prepared PEEK samples, the yield strength and elongation were 98.3 ± 0.49 MPa and 22.86 ± 2.12%, respectively. Compared with the yield strength of PEEK prepared by EM, the yield strength of PEEK prepared by FDM increased by 65.38%. The crystallinity of FDM-prepared and EM-prepared samples was calculated as 34.81% and 31.55%, respectively. Different processing methods resulted in differences in the microscopic morphology and crystallinity of two types of PEEK parts, leading to differences in mechanical properties. The internal micropores generated during the FDM processing of PEEK significantly reduced the elongation. Moreover, according to the DMA results, the glass transition activation energy of PEEK was obtained as ΔE = 685.07 kJ/mol based on the Arrhenius equation. Due to the excellent mechanical properties of PEEK prepared by FDM processing, it is promising for high-performance polymer applications in different fields.

Investigating tensile failure mechanisms of layered rocks through physical testing and PFC3D analysis

Rocks generally exhibit less resistance to tension compared to shear or compression forces, and tension cracks often precede shear or compression failures. While the mechanical performance of rock layers under compression has been widely described, their tensile behavior is less known.The current study includes experimental approaches as well as computational testing with the three-dimensional Particle Flow Code (PFC3D) to evaluate the effect of layer thickness and mechanical parameters on the strength and failure patterns of layered rocks-like materials under continuous tension.The Brazilian tensile strength test was conducted on concrete and gypsum specimens. The concrete specimen measured 54 mm in diameter and 27 mm in thickness, resulting in a tensile strength of 1.35 MPa. The gypsum specimen, with the same measurements, had a tensile strength of 0.6 MPa. In addition, uniaxial compressive strength tests were performed on both materials, yielding compressive strengths of 18 MPa for concrete and 6 MPa for gypsum. Our findings indicate that layer thickness and mechanical properties considerably influence failure patterns, tensile strength, and progressive deformation of these materials. The failure modes seen in the layered specimens indicate that the tensile strength ascertained by numerical testing and direct tensile testing is equally accurate. Both the empirical and computational findings are in accordance with the analytical predictions of the failure criterion. In rock engineering, these failure criteria have a high degree of accuracy when it comes to predicting tensile strength and reflecting the failure modes of layered rocks, like layered sandstone, slate, and shale

An overview of tensile and shear failure mechanisms of silicon carbide-based ceramic matrix composites

The successful applications of silicon carbide-ceramic matrix composites (SiC-CMCs) in aeronautical and aerospace industries require deeper understanding of their mechanical behaviors and failure mechanisms. The overview on tension and shear is then presented from meso-mechanics perspective, including matrix cracking, interface de-bonding and sliding, matrix crack propagation as well as fiber bridging. The results reveal that the matrix cracking stress is proportional to the interface sliding stress and the matrix fracture energy. The ratio of tensile to shear stress of the matrix cracking remains constant both in tension and in shear. In addition, the deflection of matrix cracks in the interface depends on the elastic modulus matching parameter, the angle between matrix cracks and interface, as well as the residual thermal stress. The matrix cracks propagate in a random or periodic pattern, which are proportional to the sliding length at the matrix cracking stress. The fiber bridging mechanism, related to the Weibull distribution of the fiber strength, determines the tensile and shear behaviors after the saturation of matrix cracks.

Tensile strength and failure mechanism of rock–cement sample: Roles of curing temperature, nano-silica and rock type

Understanding the tensile strength and failure mechanism of rock–cement interfacial transition zone (ITZ) is of vital significance to the sealing integrity of cement sheath under downhole condition. Taking advantage of multiple techniques, i.e., digital image correlation (DIC), nano-indentation, XRD-Rietveld analysis, 29Si MAS solid NMR, and SEM-EDX, this study is devoted to investigating the impacts of curing temperature, rock type, and the addition of nano-silica (NS), on the tensile strength and failure mechanism of rock–cement sample. The experimental results show that both the curing temperature and the addition of NS leads to the formation of more C-S-H, which densifies the ITZ microstructure and responsible for high tensile strength of rock–cement samples; the tensile strengths of shale-cement samples are consistently higher than those of sandstone-cement sample; the crack velocities for rock–cement samples under three-point bending tests are approximately 1 mm/s, the crack velocities for rock–cement samples are slowed down when the NS is incorporated in cement paste, but they are independent on the rock type and curing temperature.

Exploring the synergistic influence of FDM parameters and strain rate on tensile strength and failure mechanism of FDM printed PLA

Exploring the synergistic influence of FDM parameters and strain rate on tensile strength and failure mechanism of FDM printed PLA

Dynamic splitting tensile mechanical behavior of magnesia-carbon refractories under impact loading

To enhance understanding of the dynamic tensile failure mechanism of MgO-C refractories, the Split Hopkinson Pressure Bar test combined with digital image correlation techniques were utilized. The dynamic failure behavior of specimens with different heat treatments and graphite content was investigated under various impact velocities. The MgO-C specimens exhibit severer damage and a more tortuous crack path with higher impact velocity. The SiC and forsterite phases generate during heat treatment are advantageous in inhibiting crack propagation, while the formation of oxide layer makes the material more susceptible to brittle fracture. Due to the presence of microcracks, high graphite samples lead to a reduction in tensile strength, but result in a wider fracture zone, which dissipates impact energy. Compared with the significant increase of strength under compressive impact loading, the critical tensile strain rate of MgO-C is easier to achieve after which the tensile strength decreases.

Effect of test temperature on deformation microstructure and tensile property of a novel Ni-Co-based superalloy

The tensile behavior, deformation microstructures and failure mechanisms of a novel Ni-Co base precipitation-hardened superalloy, have been investigated at room temperature (RT), 450, 550, 650 and 750 °C. Deformation of the alloy at RT, 450, 550 °C is primarily mediated by dislocation slip and stacking faults while nano-sized deformation twinning is also involved at 650 and 750 °C. The yield and tensile strength decrease with increasing test temperature. In the temperature range of 450–650 °C, however, no obvious reduction in the yield strength and work-hardening rate at low strains is observed, which could be correlated to a high density of stacking faults or deformation twins. Low yield strength and work-hardening at 750 °C, could be related to the softening by thermal activation and the softening of γ′ particles caused by the repeated cutting via stacking faults or twins. However, as the testing temperature is over 450 °C, elongation of the alloy decreases significantly with increasing test temperature, which could be associated with intergranular cracking induced by stress-assisted grain boundary oxidation.

Analysis of tensile failure mechanism in intact, foliated, and cracked rocks using distinct element method: Influence of anisotropy

A thorough numerical analysis was conducted to understand the failure mechanisms and behaviour in intact rocks, foliated rocks and rocks with pre-existing cracks using the Brazilian tensile strength tests. The dominant anisotropy in rocks, especially foliated rocks like phyllites, slates and schists, as well as sedimentary rocks like sandstone, limestones and shale, leads to complex failure mechanism. The presence of cracks leads to anisotropy causing different mechanisms of failure and variation in tensile strengths of rock mass. Numerical simulations were conducted based on experimental studies of foliated phyllite and dolomitic limestone from the Tejam Group, Lesser Himalaya. The variations in failure behaviour and strength of foliated rocks were studied for samples at different foliation angle using the particle distinct element model. The simulation results show that with increase in foliation angle to the loading direction (from 0° to 90°), the peak tensile strength of rocks remains almost same for specimens with θ = 0° to 30° and then increases linearly till 90°. The influence of cracks as anisotropy was also studied by changing crack length (from 5 mm to 30 mm) and angle (from 0° to 90°). The development of failure patterns in rocks with pre-existing cracks leads to a better understanding of the failure modes and makes it possible to interpret failure behavior, pattern, and strength parameters. With increase in crack length, the tensile strength of rocks decreases. Overall, this study depicts the influence of anisotropy and microparameters on failure modes and behavior in Brazilian tensile strength tests on foliated and pre-cracked rocks.

Mechanical properties and tensile failure mechanisms of SM400A steel treated by high-power continuous-wave laser

This study systematically investigates the effects of high-power continuous wave laser (CWL) treatment on the mechanical behavior and failure mechanisms of SM400A steel, comparing these outcomes with those of untreated specimens. The findings reveal that while CWL treatment enhances surface hardness, it has minimal impact on the strength of thick structural steel components. However, excessive laser energy density leads to surface defects and softening of the microstructure, adversely affecting the material's toughness. This results in a reduction in elongation at fracture, transitioning the failure mode from ductile to brittle. The study concludes that to ensure the safe use of laser-treated structures, the laser energy density should be carefully controlled not to exceed 3000 J/cm2.

Spatial-temporal response and precursor characteristics of tensile failure on disc coal samples of different sizes combining AE, EMR and DIC techniques

Tensile fractures in deep coal and rock mass can readily trigger dynamic calamities like rock bursts, significantly impacting the safety of coal mining. To enhance our understanding of coal’s tensile failure mechanism, Brazilian splitting failure experiments were conducted on coal samples with prefabricated cracks of different sizes. Acoustic emission (AE), electromagnetic radiation (EMR) and digital image correlation (DIC) techniques were used to analyze the instability failure process and precursor characteristics of coal samples. The results showed that, for coal samples of the same thickness, the tensile strength and peak strain gradually decreased with the increase of coal sample size, whereas the elastic modulus increased gradually, highlighting more pronounced brittleness characteristics and revealing a noticeable size effect. The time-varying evolution of AE energy, EMR energy and VE (virtual extensometer) elongation during the tensile failure process of coal samples is closely correlated to the stress evolution trend, exhibiting distinct characteristics at various loading stages. The failure modes of coal samples of varying sizes exhibited a strong correlation with the spatial distribution of AE events, as well as the strain and displacement field measured by DIC. With the coal sample’s growing size, the percentage of AE high energy events rose while the total number of AE positioning events fell, the proportion of DIC strain concentration area decreased, displacement zoning characteristics became more obvious, and the critical opening displacement of cracks increased. The variance of AE, EMR and DIC related parameters in coal samples showed significant critical slowing down characteristics. Based on their response timescales, EMR energy was identified as an “Early warning”, AE energy as a “Medium warning”, and VE elongation as a “Short-imminent warning”. A comprehensive analysis of multi-parameter monitoring information proved beneficial in accurately pinpointing precursory response points of coal mine dynamic disasters, thereby enhancing monitoring precision.

Mineral composition, pore structure and mechanical properties of coal measure strata rocks: A case study of Pingdingshan Coalfield

The microstructure and mechanical properties of coal measure rocks (CMR) are critical factors in the successful geological storage of CO2. While previous research has predominantly focused on coal seams, the overlying and underlying bedrock strata are equally significant yet often overlooked. This study addresses this gap by selecting coal and adjacent strata from the Twelve Mine as representative samples. A comprehensive suite of analyses was conducted, including thin section identification, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), uniaxial compression, and acoustic emission tests. These analyses were used to determine the mineralogical composition and pore structure characteristics of the CMR, elucidate the mechanical failure mechanisms of different CMR types, and explore the relationships between rock strength, mineral composition, and pore characteristics. The findings indicate that the primary minerals in coal are clay minerals, while mudstone is composed predominantly of clay minerals and quartz, sandstone is rich in quartz and feldspar, and limestone contains significant amounts of calcite. The porosity of CMR varies between 1.73 % and 10.12 %, with 82.72 % of the pores being micro- to mesopores and the remaining 17.28 % being macropores. The pore structures exhibit fractal characteristics, with the fractal dimension of mesopores ranging from 2.581 to 2.902, and that of macropores from 2.968 to 2.997. Coal predominantly fails through a combination of tensile and shear failure mechanisms, mudstone and limestone through tensile failure, and sandstone through shear failure. Furthermore, the results suggest that rock strength is positively correlated with quartz content and negatively correlated with kaolinite content and porosity. In terms of their influence on coal rock strength, the factors in descending order of impact are kaolinite, quartz, calcite, microporosity, macroporosity, dolomite, and mesoporosity. Thus, while the mechanical properties of these rocks are primarily governed by their mineralogical composition, the pore structure also plays a significant role.

Dynamic tensile failure mechanism of hollow rocks: a numerical study based on AE moment tensors

Dynamic tensile failure mechanism of hollow rocks: a numerical study based on AE moment tensors

A comparative study on mechanical-electrical-thermal characteristics and failure mechanism of LFP/NMC/LTO batteries under mechanical abuse

Understanding the failure behaviors and failure mechanisms of lithium-ion batteries under mechanical abuse is essential for numerical reconstruction of abuse scenarios for different types of cells. This study investigates the mechanical-electrical-thermal characteristics, components tensile properties and failure mechanisms of LiFePO4 (LFP), Li(Ni0.5Mn0.3Co0.2)O2 (NMC), and Li2TiO3 (LTO) cells through indentation experiments, including ball intrusion, cylindrical intrusion, and out-of-plane compression modes at quasi-static loading rates. Additional ball intrusion experiments were conducted at varying loading rates. This study compares the effects of different material systems on battery performance under standardized mechanical abuse conditions. Post-test examinations analyze surface damage and internal component fracture morphology. Two distinct fracture modes were observed: ductile fracture and brittle fracture. The findings suggest that, under the same loading mode, LTO cells exhibit distinct failure behavior compared to NMC and LFP cells, attributed to differing material properties and resulting fracture modes during intrusion. Based on the analysis of the tensile results of the battery components, the cell fracture mode may be related to the tensile strength of the separator. The loading rate significantly impacts the mechanical-electrical-thermal performance of pouch cells, resulting in increased cell stiffness and shorter internal short circuit duration at higher loading speeds. However, the effect of loading rate is consistent across cells with different material systems.

Zinc-Induced Liquid Metal Embrittlement in Austenitic Microstructures

The problem of liquid metal embrittlement (LME) is one of the main concerns to be addressed when developing high-strength automotive steels. Although LME has been extensively investigated over the past decade, the role of LME-induced cracking on the failure mechanism of steel substrates has not been adequately explored. This study investigates the influence of LME cracking on the tensile properties and failure mechanism of an austenitic microstructure. An in-depth analysis of the LME crack propagation path revealed that the crack propagated predominantly along highangle, random grain boundaries. The detailed failure analysis showed that the Zn-coated austenitic steel failed in an intergranular mechanism without any plastic strain being applied to the grains during deformation. The results of the study indicate that stress-assisted grain boundary diffusion is responsible for the premature failure of Zn-coated austenitic microstructures at much lower tensile stresses than that of the uncoated specimen. It was found that the application of thermomechanical conditions characterized by low stress and low temperature, combined with microstructures featuring a low Zn grain boundary diffusion rate, can effectively reduce LME cracking.

Micromechanical modeling of longitudinal tensile behavior and failure mechanism of unidirectional carbon fiber/aluminum composites involving fiber strength dispersion

This paper examines the longitudinal tensile behavior and failure mechanism of a new unidirectional carbon fiber reinforced aluminum composite through experiments and simulations. A Weibull distribution model was established to describe the fiber strength dispersion based on single-fiber tensile tests for carbon fibers extracted from the composite. The constitutive models for the matrix and interface were established based on the uniaxial tensile and single-fiber push-out tests, respectively. Then, a 3D micromechanical numerical model, innovatively considering the fiber strength dispersion by use of the weakest link and Weibull distribution theories, was established to simulate the progressive failure behavior of the composite under longitudinal tension. Due to the dispersion of fiber strength, the weakest link of the fiber first fractures, and stress concentration occurs in the surrounding fibers, interfaces, and matrix. The maximum stress concentration factor for neighboring fibers varies nonlinearly with the distance from the fractured fiber. Both isolated and clustered fractured fibers are present during the progressive failure process of the composite. The expansion of fractured fiber clusters intensifies stress concentration and material degradation which in turn enlarges the fractured fiber clusters, and their mutual action leads to the final collapse of the composite.

Experimental and numerical investigations on tensile failure mechanism and load-bearing capacity of expansion anchors under pull-through failure mode in HPSFRC

Pull-through(PT) is a unique failure mode of torque-controlled expansion(TCE) anchor after being pulled out from concrete. No universal design formula is available for predicting tensile bearing capacity of anchor of PT mode. In normal concrete(NC), PT failure usually occurs at large embedment depths(Hef), which is uncommon in the field and received less attention than the concrete breakout failure. However, due to the improved mechanical performance of the substrate, the PT mode dominates for anchors in high-performance steel fiber reinforced concrete(HPSFRC) substrate (even at small Hef). In this study, to study the PT mode in HPSFRC, the results of 34 PT failures from previous tests, including testing scenarios with different anchor diameters(D), Hef, and fiber contents(vf), are analyzed. The cracking morphology and load-bearing capacity distribution of PT mode are elaborated. Further, finite element models(FEM) of anchor pullout behavior in HPSFRC is established, which accurately identified different failure modes. The calculated Nu by FEM agree well with the tested Nu. The difference in damage domain between different failure modes is mainly reflected in the unloading stage. Parametric analyses were conducted on pre-tightening torque(Tini), Hef, D, sleeve length(Lsleeve), anchor cone width, anchor cone length(Lcone), and vf to study their influences on Nu of PT mode. Except for Lsleeve and Lcone, which do not affect Nu, changes in other factors can cause linear or nonlinear changes in Nu. The non-linear relationship between Nu and experimental parameters is formulated. Accordingly, a new prediction model that can accurately predict Nu of PT mode for anchors in HPSFRC is developed, of which calibration factors are derived using probability functions.

Effects of temperature and low strain rate on tensile performance of aramid fiber bundle

AbstractIn this research, the effects of ultimate strain rate and environmental temperature on the mechanical performance of the aramid fiber bundles were experimentally investigated. The scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to detect the tensile failure mechanism of the aramid fiber bundle. The results indicated that the tensile strength, failure strain, elastic modulus, and toughness of the aramid fiber bundle were sensitive to the strain rate, which was represented as the typical bilinear monotonic relationships. In contrast, the impact of environmental temperature on the four parameters of aramid fiber bundle was more complex. The ultimate strength, failure strain and toughness of aramid fiber bundle increased with the temperature changing from −60 to 30°C, but rapidly decreased from 30 to 90°C. Finally, the dispersion of the mechanical performance was quantitatively analyzed based on the scale and shape parameters obtained from Weibull model.Highlights Tensile tests for aramid fiber bundle under different strain rates and temperatures were conducted. Strain rate and temperature effects on tensile properties of fiber bundle were quantified. Tensile failure mechanism of fiber bundle was analyzed. Dispersion of the mechanical performance was quantitatively analyzed.

Open Hole Tensile Behaviour of Sisal-Glass Reinforced Epoxy Composite

Research and development in engineering composites are advancing rapidly. The demand for lightweight materials with high specific strength in aerospace and high-energy applications makes composites a prime choice. Using composite materials to reduce structural weight is favored for energy saving and emission reduction, making them popular in automobiles and other fields. However, composites require holes for assembly and fastening in many applications, such as airplane structures and automotive parts. These holes can concentrate stress, potentially reducing tensile strength and compromising structural integrity. Notches, including holes and slots, are inevitable during assembly and may also result from impact damage during service. Ensuring safety and reliability necessitates quantifying residual properties and failure responses. Stress concentration issues will occur around holes, whether in laminates used for interior decoration, outsourced parts, or bearing components. Therefore, notch design must consider the effects on failure mode, mechanical performance, and interlayer damage distribution. This study examines the open-hole tensile behavior of sisal-glass fiber-reinforced epoxy composites, aiming to understand the impact of circular holes on their tensile strength and failure mechanisms.

Comprehensive investigation on linear friction welding a dissimilar material joint between Ti17(α+β) and Ti17(β): Microstructure evolution, failure mechanisms, with simultaneous optimization of tensile and fatigue properties

In order to advance the use of Ti17 (α+β)-Ti17(β) dissimilar material blisks produced with linear friction welding (LFW) for advanced aeroengines, detailed studies of failure mechanisms and performance enhancements of such joints were conducted. The changes in microstructure including phase transformations and dynamic recrystallization were investigated. Also, the tensile failure mechanism of the joint was investigated by in-situ tensile test using scanning electron microscopy, while the high-cycle fatigue failure mechanism was studied using quasi-in-situ electron back-scattering diffraction observations combined with transmission electron microscopy characterization. A post-weld annealing heat treatment (PWAHT) was applied for optimizing tensile and fatigue strength. Results shows that α dissolution and β continuous dynamic recrystallization (CDRX) are controlling microstructure changes during welding. Tensile loading failure is related to local dislocation slip concentration on the Ti17(β) side of the thermo-mechanically affected zone with limited α strengthening phase and low degree β CDRX; while fracture under high-cycle fatigue loading is related to equiaxed α/metastable β boundary microcracks on the Ti17 (α+β) side of the heat-affected zone, which was produced by unequal deformation between the two phases. Following PWAHT for 630 °C at 3 h, re-precipitation of secondary α occurred, which increased dislocation movement resistance in the weak areas, producing tensile and high-cycle fatigue strengths of 1196.4 MPa and 550.2 MPa, respectively, higher than those of BM-(β). In addition, an adequate plasticity of the joint with elongation of 8.7 % (82.1 % of Ti17(β)) was reached.

Effect of μ precipitation and γ′ evolution on intra-/intergranular strength of Ni-Co-Cr-based superalloys after 800 ℃ thermal exposure

The initiation of microscopic defects and the microstructural stability are crucial factors in determining the tensile strength and failure mechanism of Ni-Co-Cr-based superalloys. This study involved the long-term thermal exposure of Ni-Co-Cr-based superalloys at 800 ℃ and their elevated-temperature tensile testing at 750 ℃ to investigate the microstructural and properties evolution. A 100 h-exposure led to the formation of a significant number of μ precipitates rich in refractory elements at the grain boundaries, particularly on the large-sized γ′ precipitate surfaces. The intragranular γ′ precipitates considerably coarsened with an increasing thermal exposure duration while its volume fraction remained relatively constant. Cracks tended to nucleate preferentially at the μ phase interface during high-temperature tensile testing, leading to the breakage of the γ/γ′ precipitates and formation of pores owing to crack propagation. The dislocation motion as a deformation response of the intragranular γ/γ′ precipitates to tensile testing was dominated by a shearing mechanism, with a portion of the intragranular γ′ precipitates deforming through dislocation shearing. The primary failure mechanism during high-temperature tensile testing changed from intergranular to intragranular with an increasing exposure time. Investigating the relationship between the phase evolution and failure mechanism will enhance our understanding of the fracture behavior of Ni-Co-Cr-based superalloy hot-end structural parts.