Bending Fracture Behavior Research Articles

Bending deformation behavior of a 1000 MPa grade dual-phase steel with superior bending toughness

Poor bending toughness is still a critical drawback of high-strength ferrite-martensite (F-M) dual-phase (DP) steel, which is unfavorable to their collision safety. In this study, a 1000 MPa grade F-M DP steel with excellent bending toughness was fabricated by reducing the strength difference between ferrite and martensite via introducing solid solution strengthening (Si), precipitation strengthening (VC) and reasonable tailoring high martensite content. The obtained DP steel exhibits a high ultimate tensile strength (UTS) of 1123 MPa, together with a good total elongation (TE) of 16.0 % and an excellent maximum bending angle (αf) of 98°. The αf of the obtained DP steel is obviously higher than that of 62–80° for reported DP steels with similar UTS levels. The related bending deformation and fracture behavior are emphasized and indicate that high bending toughness in obtained DP steel can be attributed to the excellent coordinate deformation between ferrite and martensite, improved martensite deformability and crack blocking by the fibrous deformed martensite.

Effect of transparent polymer encapsulation overlayers on bending fracture behavior of flexible organic lead halide perovskite thin films

Although halide perovskites have significant potential for flexible devices, the bending mechanical behavior of halide thin films has not been investigated in detail. Herein, we report the quantitative bending fracture behavior of flexible methylammonium lead triiodide (MAPbI 3 ) thin films encapsulated with an overlayer of either polystyrene (PS) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The significantly retarded cracking behavior of the halide films demonstrated that adjusting the polymer overlayers with different thicknesses resulted in substantial mechanical enhancements. For example, the minimum strain for crack initiation was ~1.96% for a highly concentrated PS overlayer with a thickness of ~50 nm, which corresponds to an increase of ~40% relative to the non-encapsulated sample. In addition to quantifying the fracture behavior with fracture energy and film strength, the chemical effects of encapsulation were also investigated in terms of the phase dissolution of the perovskite, which was correlated with changes in the Hall electrical properties. • Bending fracture behavior of polymer-encapsulated perovskite halide films is studied. • Less cracks were observed with the thicker polystyrene overlayer under bending. • A 50 nm-thick polystyrene layer resulted in a 96% improvement of fracture energy. • Phase dissociation with atmospheric exposure was suppressed by polymer-encapsulation. • Hall electrical resistivity was correlative to the level of phase dissociation.

A Comparative Study for High-Cycle Bending Fatigue Lifetime and Fracture Behavior of Extruded and Additive-Manufactured 3D-Printed Acrylonitrile Butadiene Styrene Polymers

A Comparative Study for High-Cycle Bending Fatigue Lifetime and Fracture Behavior of Extruded and Additive-Manufactured 3D-Printed Acrylonitrile Butadiene Styrene Polymers

Bending Fracture Behavior of Flexible Organic Lead Halide Perovskite Films Depending on Composition and Morphology

Organic-inorganic halide perovskites receive great attention due to their superb optoelectronic properties such as high efficiency over 25% demonstrated on a glass-based solar cell. Since flexible optoelectronics are considered to be more beneficial to territorial and space applications than the rigid counterparts due to lightweight and bendable characteristics, flexible perovskite optoelectronics need to be developed. However, mechanical properties of perovskite films depending on compositions has not been studied. We report here on bending fracture behavior of the flexible perovskite films depending on the substitution ratio (x) in four different compositions of (FAPbI3)1-x(CsPbBr3)x, (FAPbI3)1-x(MAPbBr3)x, FA1-xCsxPbI3, and FA1-xMAxPbI3 (FA = formaminidinium). The spin-coated perovskite films on the indium-tin-oxide (ITO)-coated polyethylene naphthalate (PEN) substrates show different morphology depending on x and composition. At certain values of x, that is mixed cation and/or mixed anion, a wrinkled morphology is obtained with different amplitude and wavelength in the sinusoidal surface structure. Based on applied and critical strains, fracture energy and fracture toughness are estimated, where the mixed compositions with enhanced wrinkled morphology show an improved bending fracture behavior as compared to the pure FAPbI3 or MAPbBr3. The highest fracture energy of 186.2 J/m2 along with fracture toughness of 3.559 GPa∙(m1/2) is obtained from (FAPbI3)0.75(CsPbBr3)0.25 due to highly enhanced wrinkled morphology.

High cycle rotating bending fatigue performance and fracture behavior in a pearlite–ferrite dual-phase steel

High cycle rotating bending fatigue performance and fracture behavior in a pearlite–ferrite dual-phase steel

Bending Fracture Behavior and Chemical Degradation of Polymer-Passivated Flexible Organic Lead Halide Perovskite Thin Films

Although halide perovskites have significant potential for flexible electronic and optoelectronic devices, detailed bending mechanical behavior of encapsulated halide films has not been reported yet. Herein, we report the enhanced bending fracture behavior of flexible methylammonium lead triiodide (MAPbI3) thin films passivated with two selected polymer over-layers of polystyrene (PS) and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The substantial mechanical enhancements were evident from the estimated fracture parameters, including critical strain, fracture energy, and film strength. For example, a highly concentrated PS passivation layer with ~51 nm thickness exhibited the largest fracture energy of 60.4 Jm-2 and the highest film strength of 299.9 MPa, which correspond respectively to ~96% and ~40% improvements compared to those of the non-passivated reference. Effects of the chemical passivation was also confirmed by chasing phase-dissolution of the perovskite with correlative changes of Hall-electrical properties.

Characterization of bending behavior of hydroxyapatite/biopolymer porous composite beams

In this work, porous composite beams of HA/PLLA and HA/PLCL were developed using a combination of the template and freeze-drying methods. Their compositions were examined using Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy. Their bending mechanical and fracture properties were characterized under the three-point bending condition. Their microstructures and the micro mechanisms of deformation and fracture were also examined by scanning electron microscopy. It was confirmed that the presence of polymer material did not affect the crystal structure of HA, and the diffraction pattern of both beams remained the same after sintering. Both composite beams showed dramatically improved flexural mechanical properties compared to a pure HA beam. Their bending fracture behavior was characterized as a crack initiation and growth accompanied by microdamage formation at the center. It was determined that microdamage formation and the subsequent deformation and fracture of the polymer phase was initiated by microfracture of HA struts. It was also found that the addition of PLLA results in a higher modulus and fracture strength, while the addition of PLCL results in a higher fracture energy due to ductile elongation.

Halide Perovskites: Anisotropic In Situ Strain‐Engineered Halide Perovskites for High Mechanical Flexibility (Adv. Funct. Mater. 4/2021)

In article number 2007131, Yong Soo Cho, Da Bin Kim, and Jung Won Lee propose an in-situ strain engineering method to substantially enhance the bending fracture behavior of flexible halide perovskite films. The strain-dependent mechanical properties with structural simulations are extensively useful for halides-based electronic and optoelectronic devices.

Study on the Long Bone Failure Behaviors Under the Indenter Rigid-Contact by Experiment Analysis and Subject-Specific Simulation.

The bending fracture behaviors of long bone have gained great attention due to the high bending fracture risk during sports events, traffic accidents, and falling incidents, etc. For evaluating bone bending behaviors, most of the previous studies used an indenter in three point bending experiments while the effect of its rigidity was never considered. In this work, using the porcine long bones, the three point bending tests were conducted to explore the bone fracture behaviors under a rigid indenter. In addition to collecting the force applied, the bone fracture dynamic process was recorded by high-speed photography, and the fracture surface profile in mesoscale was observed by the scanning electron microscope (SEM). Based on CT scanning of long bones, the cross section properties of test specimens were calculated by a homemade matlab script for correlating with their failure strengths. Also, a subject-specific finite element (FE) model was developed to identify the outcomes induced by a rigid indenter on simulation. Findings led to conclusions as follows: (1) The tension fracture came with fracture path deflection, which was caused by the bone indentation induced mesoscale crack-opening. Due to this damage before the whole bone fracture, a bone fracture moment correction was established to compensate experimental data. (2) The plastic indentation caused the force fluctuation as suggested by correlation analysis. (3) The bone failure moment correlated with the inertial moment of the bone cross section at the fracture location higher than the traditional cross section area. (4) In the subject-specific simulation, the indentation caused compression fracture under a much lower failure force. Removing the element erosion on the indenter-contacted area only during the validation was verified as a good option to solve this issue.

Bending Properties and Failure Mechanism of Continuous W-Core-SiC Fiber-Reinforced 2024 and 6061 Aluminum Matrix Composites

In order to investigate the effect of different matrices on the bending properties and fracture behavior of the continuous W-core-SiC fiber-reinforced aluminum matrix (SiCf/Al) composites, 30 vol.% SiCf/2024Al and 30 vol.% SiCf/6061Al composites were prepared via matrix coating and hot isostatic pressing. Samples from these composites were subjected to the push-out test and three-point bending test with in situ SEM. The microstructure of the SiCf/Al composites was examined by SEM and TEM. Results showed that there were coarse AlCuFeMn and Al2Cu phases in the matrix of the SiCf/2024Al composite, and needle-like Al4C3 phase at the interface between fiber and matrix. For the SiCf/6061Al composite, there were no coarse second phase in the matrix and no Al4C3 phase at the interface between fiber and matrix. The interfacial shear strength of the SiCf/2024Al composite (~ 37 MPa) was relatively larger than that of the SiCf/6061Al composite (~ 34 MPa), indicating a relatively strong interface bonding for the SiCf/2024Al composite. The bending strength of the SiCf/6061Al composite (1091 MPa) was superior to that of the SiCf/2024Al composite (968 MPa). For 30 vol.% SiCf/2024Al composite, cracks were initiated at the edge of the coarse second phase under bending load and propagated along the grain boundary of matrix. The crack passed directly through SiC fibers due to the strong interface bonding and needle-like Al4C3 phases formed by interfacial reaction, and the propagation rate was fast. For 30 vol.% SiCf/6061Al composite, the crack was initiated at the interface between fiber and matrix when the plastic deformation of matrix was retarded at the first SiC fiber. Then, the crack passed around SiC fibers and propagated in forms of crack bridging and deflection due to the suitable interface bonding, and the propagation rate was slow.

Bending fracture behavior of freestanding (Gd0.9Yb0.1)2Zr2O7 coatings by using digital image correlation and FEM simulation with 3D geometrical reconstruction

It is important to investigate the mechanical performances of (Gd0.9Yb0.1)2Zr2O7 (GYbZ) materials deposited on irregular substrates for improving new thermal barrier coatings. Three-point bending fracture characteristics of freestanding GYbZ coating prepared by supersonic plasma sprayed (SPS) technique were investigated with the help of digital image correlation technique. The cracking time, crack propagation path, and mechanical properties of GYbZ coating were obtained. Meanwhile, the X-ray computed tomography technique was introduced to scan the microstructure of freestanding GYbZ coatings, which are used to establish three-dimensional (3D) finite element model by using the Avizo software. The brittle cracking criterion was applied to describe the bending fracture process of GYbZ coatings. The critical cracking strain was estimated as 0.36%±0.03% by repeatedly comparing the difference between the experimental and simulated curves. The results would be extended to predict the dangerous region and failure mechanisms of GYbZ coatings deposited on irregular substrate during finite element simulations.

Effect of laser cladding and laser-induction hybrid cladding coatings on the bending properties and fracture behavior of rails

Laser cladding (LC) and laser-induction hybrid cladding (LIHC) technologies, with low dilution, low deformation and high deposition efficiency, have attracted a lot of notices in repairing and hard-facing the full-scale rail. However, the cladded coatings with different microstructure and properties will also affect the bending stress distributions of rails during service, which may lead to the rails' failure and fracture. In this paper, the bending properties and fracture mechanisms of rails deposited by LC and LIHC were studied systemically by the three-point bending tests coupled with finite element method simulations (FEMS). The results indicate that the ultimate bending strength (UBS), fracture strain (εf) and fracture work (W) of the specimen by LIHC are about 1.35, 4.28 and 7.70 times of that by LC correspondingly. The dramatically difference is mainly caused by the heat affected zones (HAZs) induced by different technologies. Under the bending stress, both the maximum stress and initial damage of the specimen by LC generate in the HAZ, while the cracks extend intergranularly in HAZ and lead to the rapid overall instable fracture. Oppositely, the initial damage of the specimen by LIHC originates from the surface on the tension side where the maximum stress generates, and the HAZ by LIHC is proved to be able to promote both the bending strength and fracture toughness of the rail. On the other hand, the thickness and properties of the cladded coatings are the main factors affect the bending properties of specimens by LIHC. When the parameters are chosen suitably, both the yielding strengths and UBSs of specimens by LIHC are even higher than that of the rail substrate, which means LIHC can adjust the rail's performances reasonably while prevent the rail from bending fracture.

Improved Bending Fracture Behavior of Large-Scale Graphene Monolayer-Intervened Flexible Oxide Thin Films

This work describes for the first time the quantitative analyses of bending fracture resistance of a flexible transparent conducting oxide (TCO) thin film, here using Al-doped ZnO thin films, which are substantially improved by the intervention of a monolayer graphene layer. Most of the mechanical effects by graphene have focused on the graphene itself and particularly when only the stretched strains are applied. Excessive stretching stress induces buckling and/or flakes with the intervened graphene, which has been the issue for the actual evaluation of flexible cracking performance. This work focuses on the external effect of graphene, namely how the intervention of graphene can influence positively the fracture behaviour of inorganic thin films under bending operation on the basis of quantitative analyses of flexible fracture parameters including fracture energy, film strength and fracture toughness. A graphene monolayer of ~1 cm x 1 cm scale was transferred successfully to a polymer substrate prior to the sputter-deposition of Al-doped ZnO thin films with variable thickness of 50 to 200 nm. Cracking evolution of the ZnO:Al thin films depended largely on the applied bending strain and film thickness. The crack-initiating strain of ~1.64% with the graphene corresponds to a ~61% improvement compared to the reference sample without the graphene. The resultant mechanical parameters, fracture energy, film strength and fracture toughness, support well the enhanced fracture resistance under the bending operation. For example, the fracture energy was identified as enhanced by ~272% with the intervention of graphene.

Effect of heat treatment on interface behavior of martensite/austenite multilayered composites by accumulative hot roll bonding

ABSTRACTThe 2Cr13/316L multilayered steel (MLS) composites were prepared by accumulative hot roll bonding and heat treatment. The element diffusion, interface bonding mechanism and interface bonding properties of the MLS composites were investigated. The microstructures of the MLS composites before and after heat treatment, are mainly composed of austenite (A), martensite (M), ferrite (F) and little M23C6 carbides. The grain refinement is achieved by accumulative hot roll bonding and heat treatment. The bonding mechanism can be divided into diffusion and recrystallization based on the difference of formation of interfacial grains. The heat treatment has opposite effects on bending strength and shear strength, it is because that softening and interface enhancement of heat treatment have different effects on corresponding bending and shear fracture behavior.

Fundamental Differences between Fracture Behavior of Thin Sheets under Plane Strain Bending and Tension

A numerical investigation of thin sheets under plane strain tension and bending is presented. Bending simulations are based on a VDA plane-strain bending test while tensile simulations depict a notched plane-strain tensile coupon. A comparative analysis of the stress and strain distributions inside the localized zone of deformation is performed for two investigated modes of behavior. The analyses suggests significant stress state differences in bending and tension driven primarily by the through-thickness response. The results offer insight into fundamental differences in tensile and bending fracture behaviors of thin sheets, as evidenced by discrepancies in strain at fracture experimentally measured using notched tensile coupons comparing to VDA bend tests. The consequences of these differences for material characterization and model calibration for large-scale crash simulations are also briefly discussed.

Bending property and fracture behavior of continuous glass fiber-reinforced PEEK composites fabricated by the wrapped yarn method

The purpose of this study was to investigate bending properties and fracture behavior of the unidirectional continuous glass fiber-reinforced poly(ether ether ketone) composites based on the wrapped yarn method and to obtain an optimum fabrication condition. The composite plates were fabricated at different processing conditions, and their bending properties and fracture behaviors were investigated in terms of thermal, morphology, and fracture characterizations. The results indicate that the cooling rate lightly affected the bending performance; however, both molding temperature and holding time had a significant effect on the bending performance. Specifically, increasing the molding temperature or the holding time was conductive to reducing the delamination.

Quantitative analysis of improved bending fracture behavior of large-scale graphene monolayer-intervened flexible oxide thin films

A graphene layer improves the fracture resistance of flexible transparent conducting films by ∼61%.

Evaluation of high-cycle bending fatigue and fracture behaviors in EN-GJS700-2 ductile cast iron of crankshafts

Abstract In this article, high-cycle bending fatigue and fracture behaviors of the EN-GJS700-2 ductile cast iron, which has been widely utilized for crankshafts in engines, was experimentally evaluated. For such objective, standard specimens were extracted from the crankshaft and examined by the four-point rotary-bending high-cycle fatigue testing machine. Then, the S-N curve was evaluated for the studied material. Experiments were followed by the fracture investigation, using the scanning electron microscopy. Then, Obtained results indicated that high-cycle fatigue lifetimes were lower than the S-N curve from the FEMFAT data bank, since standard specimens were extracted from the crankshaft to consider the manufacturing effect. The failure analysis indicated different observations including striation marks (according to cyclic loading), debonding of nodular graphites from the ferritic-pearlitic matrix (as an evidence of the plastic deformation), micro-cracks and the secondary crack (near nodular graphites), cleavage marks (due to the brittle fracture), scratching marks (resulted from the friction and striking between two fracture surfaces) and inclusions.

Quantitative analysis of bending fracture resistance of nanoscale Cu-buffered ZnO:Al thin films on a polymer substrate

Improving the fracture resistance of fragile inorganic thin films under various bending conditions is critical in flexible thin-film systems. Here, we introduce a Cu-buffer-layer approach to evaluate the level of enhancement in the bending fracture behavior of Al-doped ZnO (AZO) thin films on the basis of quantitative mechanical parameters such as fracture energy, film strength and fracture toughness. These fracture behaviors of thin films sputter-deposited onto polyethersulfone substrates were observed to depend largely on the thickness of the Cu buffer layer. In the case of thin films with a 20 nm-thick Cu buffer layer, crack-initiating bending strain was substantially improved from ∼1.04% to ∼1.37%; this corresponds to an improvement of ∼31.7%. The substantial improvement is attributed to the presence of the Cu buffer layer, which helps prevent the formation of cracks by absorbing crack-initiating tensile stress. The calculated values of fracture energy and film strength support well the Cu thickness dependence of fracture behavior under bending operation.

Mechanical bending strength of (Bi0.5Na0.5) TiO3-based lead-Free piezoelectric ceramics

(Bi0.5Na0.5)TiO3 [BNT] is expected as one of candidate lead-free materials because these ceramics show relatively good high-power piezoelectric properties. In this study, we tried to understand the bending strength and fracture behavior of the BNT-based ceramics. To measure the bending strength, a three-point bending test on the basis of JIS was conducted using 12.0 × 4.0 × 1.0 mm3 specimens. An average bending strength, σA, of pure BNT ceramics sintered at 1100 °C for 2, 12 and 24 h were 217, 195 and 187 MPa, respectively. It is cleared that the σA increased with decreasing the sintering time, (grain size and pore size). We also investigated the bending strength of Nb2O5 doped BNT ceramics [BNT-Nb x, x = 0.05 ∼ 1.5 wt%] and MnCO3 doped BNT ceramics [BNT-Mn x, x = 0.5 and 1.0 wt%]. Values of the σA of BNT-Nb 0.5 and BNT-Mn 0.5 were 222, and 188 MPa, respectively. It is clarified that soft dopants (Nb) can improve the bending strength of BNT-based ceramics. Additionally, hot-pressed BNT [HP-BNT] were sintered at 1050 °C for 5 h, and the σA of HP-BNT was 245 MPa.