Notch Bend Research Articles

Toughness Amplification via Controlled Nanostructure in Lightweight Nano-Bouligand Materials.

The enhanced properties of nanomaterials make them attractive for advanced high-performance materials, but their role in promoting toughness has been unclear. Fabrication challenges often prevent the proper organization of nanomaterial constituents, and inadequate testing methods have led to a poor knowledge of toughness at small scales. In this work, the individual roles of nanomaterials and nanoarchitecture on toughness are quantified by creating lightweight materials made from helicoidal polymeric nanofibers (nano-Bouligand). Unidirectional ( = 0°) and nano-Bouligand beams ( = 2°-90°) are fabricated using two-photon lithography and are designed in a micro-single edge notch bend (µ-SENB) configuration with relative densities between 48% and 81%. Experiments demonstrate two unique toughening mechanisms. First, size-enhanced ductility of nanoconfined polymer fibers increases specific fracture energy by 70% in the 0° unidirectional beams. Second, nanoscale stiffness heterogeneity created via inter-layer fiber twisting impedes crack growth and improves absolute fracture energy dissipation by 48% in high-density nano-Bouligand materials. This demonstration of size-enhanced ductility and nanoscale heterogeneity as coexisting toughening mechanisms reveals the capacity for nanoengineered materials to greatly improve mechanical resilience in a new generation of advancedmaterials.

Interlaminar performance of 3D CNTs/carbon black film enhanced GFRP under low-temperature cycling

Unidirectional Glass Fiber Reinforced Plastic (GFRP) laminates were prepared by inserting three-dimensional (3D) CNTs/carbon black film or CNTs/graphene oxide (GO) film into the laminates to improve the interlaminar performance. The effects of low-temperature cycles (35 cycles between −58 °C and room temperature (RT)) on the samples were investigated, and the damage caused to the reinforcement layer was directly detected by comparing the interlaminar images. By comparing the experimental results of the double cantilever beam (DCB) and end notch bending (ENF) test, the optimising effect of the new composite film (CNTs/carbon black film) on the interlaminar fracture toughness was verified. The results showed that the interlaminar fracture toughness of CNTs/GO film and CNTs/carbon black film in modes I (ENF test) and II (DCB test) was similar and superior to that of CNTs film. Regarding the effect of the low-temperature cycles on the samples, the change of CNTs/carbon black film and CNTs/GO film is also lower than that of CNTs film. Finally, the matrix interface and failure mechanisms of the interlaminar reinforcement were investigated by scanning electron microscope (SEM).

Fracture toughness and progressive damage mechanisms of 2.5D woven SiCf/SiC composites

This paper presents the effects of matrix and interface on the fracture toughness and progressive damage mechanisms of 2.5D woven SiCf/SiC composites. Third-generation SiC fibers were selected. 2.5D woven SiCf/SiC composites with four interfacial layers PyC, PyC/SiC, BN, BN/SiC and two matrix polycarbosilane (PCS) and liquid hyperbranched polycarbosilane with vinyl groups (VHPCS) were prepared by a combination of chemical vapour deposition (CVD), chemical vapor infiltration (CVI), and precursor infiltration pyrolysis (PIP) processes, respectively. Single edge notch bending (SENB) tests were carried out to investigate the fracture toughness. Moreover, acoustic emission (AE) and X-ray micro-computed tomography (Micro-CT) techniques were employed to analyze the progressive mechanical properties and failure mechanism. Results showed that the matrix and interface have significant effects on the fracture toughness. Moreover, 2.5D woven composites with PyC/SiC interfacial layers and VHPCS matrix have the highest fracture toughness (16.93 ± 1.20 Mpa • m1/2). Furthermore, during progressive damage, the pores can influence the crack expansion path, and effectively regulate the stress concentration and increase the toughness of the composites.

Fracture toughness of nano-zirconia filled aluminum matrix composites: an experimental and numerical analysis

During the service life of components, they encounter several cyclic loadings that consequently generate stress which encourages crack interaction ultimately deteriorating materials’ performance. The present study aims to investigate the fracture behaviour of aluminium 6061 reinforced with 0–15 wt% ZrO2 particles (at step of 5 wt%) fabricated using stir casting technique. Compositional analysis through x-ray diffraction was performed on the prepared composite samples. The fracture toughness of prepared composites is investigated through bending test by using single edge notch bend (SENB) specimens. In addition, the computation of fracture toughness was also performed by finite element analysis (FEA) approach, and the numerical results obtained from the FEA were compared with the experimental value. Furthermore, fractography and microstructural tests were carried out in order to investigate the influence of reinforcement weight percentage on the failure behaviour of the composites that had been prepared. The results show that with inclusion of ZrO2 (15 wt%) in aluminum 6061 matrix the maximum fracture toughness of 500.83 MPa.mm0.5 was observed. The study performed through FEA highlights the stress phenomena and result are in good agreement with the experimental results.

Analytical and finite element analysis of the concrete stress intensity factor with carbon fibers

Concrete is a material with low tensile strength and fracture resistance. One way to improve these properties is through the insertion of synthetic fibers such as carbon fibers into the concrete. This work determined the stress intensity factor for concrete with aligned carbon fibers (laminate) using an analytical model and finite element methods – macro-mechanical analysis of the composite laminate using the ABAQUS finite element package. Symmetrical laminate models were used with carbon fibers ranging from ± 15° to ± 75°. A single-edge notch bending specimen geometry was used to determine the KI of the laminates. The mechanical properties of the laminate were obtained through analytical models of the laminate theory. Results indicate that the fiber angles influence the stress intensity factor. The behavior is practically linear and a strong correlation was observed between the angle of the fibers and the KI through Pearson’s r. The laminate with a fiber angle of ± 75° showed a higher KI value compared to the others (x14 about ± 15°). Comparisons of the analytical and numerical results showed good agreement in the determined KI.

Influence of the bi-nonlinearity on the characterization of mode I fracture parameter [formula omitted] for a cracked giant magnetostrictive material in the coupled magneto-elastic field: An experimental and numerical study

Terfenol-D, a giant magnetostrictive material exhibits bi-nonlinear stress-strain relationship in coupled magneto-elastic field. A novel hyperbolic vector generalized magneto-elastic constitutive model is employed to describe this bi-nonlinear stress-strain behaviour. Some physics-based experiments for magnetization and magnetostriction hysteresis loops and mechanical compression tests under the applied magnetic field are conducted. The general HM and stress-strain relationships are programmed in C language to define the coupled field constitutive material model. Coupled magneto-elastic response from the performed finite element analyses are compared with experiments to optimize the material parameters. Fracture experiments employing single edge notch bend (SENB) specimens are conducted with and without external magnetic field as per ASTM E399. The digital image correlation technique is used to capture the load line and crack opening displacement variation with peak fracture load data. Two parameter Weibull statistical theory of strength has been utilised to forecast the mean peak fracture load. The Weibull modulus and goodness of fit are assessed using linear regression analysis (LIN2), biased and unbiased maximum likelihood estimation (MLE2-B & MLE2-U) approach. Finite element crack propagation model based on the optimized nonlinear constitutive relations is built concerning to magnetization and stress dependent elasticity problem of Terfenol-D fracture. Three-dimensional J-integral is formulated considering the effects of magneto-elastic fields, which is subsequently used to characterize the crack front singularity near the fracture process zone. Critical strain energy release rate JIc was calculated using the mean peak fracture load in both absence and presence of the external magnetic field. Finally, the influence of bi-nonlinear modularity and applied external magnetic field on the fracture behaviour of the Terfenol-D SENB fracture specimen were compared with the unimodular experimental results and substantial differences were reported. The stipulation and importance of considering the bi-nonlinear critical strain energy release rate JIc in the context of a coupled magneto-elastic field was discussed certifying the observations.

Influence of constituent particles on fracture of aluminum alloys under high-triaxiality loading

Single-edge notch bending tests are conducted to study the influence of constituent particles on the fracture resistance of aluminum alloys 6061, 6063, and 6110 under high-constraint loading conditions. The alloys are tested in the as-cast state after homogenization and artificial aging to temper T6. Each alloy type was delivered with two different volume fractions of constituent particles to enable a quantitative assessment of its impact on the toughness of these aluminum alloys. One variant corresponds to the commercial alloy, whereas the other variant is tailor made with an increased amount of constituent particles by adding Fe and Si to the commercial alloy. All alloys exhibit a dendritic structure with particles clustered at grain boundaries and dendrite arm boundaries. The increased content of constituent particles in the tailor-made alloys is shown to be purely detrimental for the toughness and reduces relevant fracture energy parameters by more than 50% in the alloys tested herein. In the plane-strain-dominated regions of the specimens where the stress triaxiality is highest, crack propagation was found to take place on grain boundaries and dendrite arm boundaries due to void nucleation, growth, and coalescence from the constituent particles. Differences in toughness between the alloys are primarily related to variations in the content, size, and spacing of the constituent particles. A comparison between the three different alloy types, i.e. 6061, 6063, and 6110, shows that strength affects the toughness, but it does not follow the commonly reported trade-off between strength and ductility.

Characterization of the non-isotropic tensile and fracture behavior of unidirectional polylactic acid parts manufactured by material extrusion

This study presents a comprehensive characterization of the fracture and tensile behavior of unidirectional polylactic acid (PLA) parts manufactured by material extrusion (MEX). The effect of the crack tip to filament orientation angle on the fracture behavior was investigated through three-point bending on single-edge notch bending (SENB) specimens printed at seven different build angles. The fracture test results show a brittle behavior for inter-layer fracture and a more ductile behavior for cross-layer crack propagation. Specimens with a 20° build angle required the most energy for the crack to extend completely, exhibiting mixed cross- and inter-layer crack propagation. The elastic properties and the ultimate strength distribution were measured through tensile tests on dogbone specimens printed at five different build angles. The experimental stiffness and strength distributions show good agreement with the orthotropic material model and the Tsai–Hill strength criterion, with a maximum model error of ≈ 10%. The printed mesostructures and the fracture surfaces were observed with scanning electron microscopy (SEM). Finally, differential scanning calorimetry (DSC) was used to evaluate the level of crystallinity in the printed structures. The resulting data allows the development of fracture models able to capture the complete failure behavior of MEX fabricated parts.

The influence of constraint on fracture toughness: Comparing theoretical [formula omitted] shifts in master curve analyses with experimental data

Quantifying the relationship between crack tip constraint and fracture toughness is key to improving the structural integrity assessment of critical infrastructure. The role of in-plane and out-of-plane constraint on fracture toughness requires greater understanding, particularly for low strength materials where test data are limited. In this work a structural steel, grade S275, is assessed both experimentally and via computational methods to investigate the role of constraint on fracture toughness. Single edge notch bend (SENB) samples, tested under three point bend conditions, at temperatures within the ductile-to-brittle transition range (+20 °C to −70 °C) are presented. Both standard (B=W, B=0.5W) and non-standard (B=0.75W, B=0.25W) bend test geometries are assessed. Here it is shown that the in-plane and out-of-plane constraint parameters are interdependent. Out-of-plane (thickness) constraint trends which are generally accepted to occur under high in-plane conditions are not present when the in-plane constraint is reduced. The amount of ductile tearing incurred during fracture toughness testing is typically greater when both in-plane and out-of-plane constraint is reduced. Thin samples are shown to be more ductile than thicker samples for equivalent in-plane conditions. These findings are relevant to pressurised components operating at low temperatures.

Investigations on fracture characteristics of Aluminium 6082-T6 alloy by Using Single Edge Notch Bending

Aluminium 6082-T6 is a structural alloy having high strength has seen replacing 6061 alloy in engineering applications. During manufacturing process geometric discontinuities are inevitable. The presence of notch in the component is more dangerous. In this paper, the influence of notch length on miniature fracture characteristics of aluminium 6082-T6 alloy has been studied. Experiment was carried in accordance with ASTM standard and specimens were tested by varying the notch length within the specified constraint. Single edge notch bending test was performed on each of specimens under mode-I condition. Results showed that the specimen with minimum notch length has high crack tip initial instability, further increase in the notch length leads to decrease the load carrying capacity, extended portion of crack length and nature of fracture. On experimental observation, plastic zone size near the end of the cut is majorly dependent on notch length of the specimen. The fractured surface analysis also carried on selected specimen with the help of scanning electron microscope. Overall results shows that crack growth and crack propagation vary as a function of notch length and is different in each of the specimens.

Fatigue crack non-propagation behavior of a gradient steel structure from induction hardened railway axles

Abnormal damages in railway axles can lead to a significant hazard to running safety and reliability. To this end, a surface treatment was selected to effectively inhibit fatigue crack initiation and growth. In this study, a single-edge notch bending fatigue test campaign with artificial notches was conducted to elucidate the fatigue crack non-propagation behavior in railway S38C axles subjected to an induction hardening process. The fatigue cracking behavior in the gradient structure was revealed by optical microscopy, electron backscatter diffraction, and fractography. The microhardness distribution was measured using a Vickers tester. The obtained results show that the microhardness of the strengthening layer is nearly triple that of the matrix. Owing to the gradient microstructures and hardness, as well as compressive residual stress, the fatigue long crack propagates faster once it passes through the hardened zone (approximately 2.0 mm in the radial depth). Thereafter, local retarding (including deflection, branching, and blunting) of the long crack occurs because of the relatively coarse ferrite and pearlite in the transition region and matrix. Totally, this fatigue cracking resistance is reasonably believed to be due to the gradient microstructure and residual stress. These findings help to tailor a suitable detection strategy for maximum defects or cracks in railway axles.

Harnessing the thermo-mechanical properties and toughness of MWCNT/TiO2 hybrid epoxy nanocomposites

One of the significant challenges of developing high-performance polymer nanocomposites is the best exploitation of the potential of nanofillers. In this study, the multi-walled carbon nanotubes (MWCNTs) are exfoliated by TiO2 nanoparticles using ultrasonic waves. The obtained MWCNT/TiO2 hybrid nanofiller, in different wt.%, is infused into an epoxy (EP) matrix using an ultrasonic dual mixing (UDM) technique to obtain multifunctional nanocomposites with enhanced thermo-mechanical properties and toughness. XRD crystallography, Raman spectroscopy, TEM analysis, TGA, DMA, tensile, and 3-P single edge notch bending tests are used to investigate the properties of the MWCNT/TiO2 hybrid nanofiller and resulting composites. Results reveal that the optimum loading of MWCNT/TiO2 hybrid nanofiller (1.0 wt.%) in EP matrix provides 23.5%, 39.8%, and 46.8% improvement in storage modulus, tensile strength, and fracture toughness, respectively, compared to those of neat EP. The FESEM images of the fractured surface of nanocomposite specimens confirm the cluster-free distribution of MWCNTs in the EP matrix ensuring enhanced thermo-mechanical properties and toughness.

Micromechanical modelling of API X80 linepipe steel

Gurson–Tvergaard–Needleman (GTN) model parameters have been estimated for the API X80 linepipe steel; these parameters and mesh size are transferable from one geometry to another. Fracture data are non-transferable from the lab specimen to the component level. These issues are resolved by local approaches to fracture to predict damage. GTN model incorporates the local features of the fracture, i.e., nucleation, growth, and coalescence of voids. The void volume fraction of material at different stages of loading governs the load-carrying capacity. This research has explored the methodology to determine the parameters by metallographic examination, known as micromechanical modelling. Parametric study and calibration of the parameter are done to fit the load-displacement curve of the notched tensile bar. These parameters are validated on the single edge notch bend (SENB) test. Estimated GTN parameters can predict the damage behavior for moderate to low constraints; hence, these parameters and mesh size are transferable from one geometry to another.

On the applicability of digital image correlation method in extracting the higher order terms in stress field around blunt notches

Accurate and deep understanding of the stress field has a key role in designing and optimizing the engineering structures. The main objective of the present article is to experimentally investigate the stress field around various blunt notches by means of the digital image correlation (DIC) method. First, several mode I tests were conducted using two types of specimens, namely single edge notch tension (SENT) and single edge notch bending (SENB), each consisting of three different notches (U, VO, and Keyhole). Then, the optical method of DIC was used to determine the stress field around the notch tip by calculating the coefficients of singular and higher-order terms (HOTs) for each notch type. To do so, the output displacement field of the DIC measurements was considered as input data for a computer program, and the coefficients of the stress field were calculated by the least square method (LSM) and an over-deterministic approach. Moreover, the effects of several geometry parameters like notch opening angle and notch tip shape on the stress distribution around the notch were discussed in detail. Finally, the precision of the calculated notch stress intensity factors (NSIFs) and the coefficients of HOTs were studied by comparing the DIC results with those obtained from the finite element (FE) analysis. It is also shown that HOTs of stress field have considerable contribution in more precise determination of the stress field around notches.

Mechanical Testing Methods for Evaluating Thermoplastic Permanent Pavement Markings

The durability of permanent pavement markings (PPMs) on roadways is important for drivers’ safety. There are two primary mechanical failure modes: cohesive failure that occurs internally in PPMs through small defects, such as internal pores, and adhesive failure that occurs along the interface between PPMs and road surfaces. Thus, it is critical to characterize the intrinsic mechanical properties of PPMs as well as the adhesion of PPMs on road surfaces to understand their mechanical performance and, ultimately, the durability of PPMs. In this study, the flexural modulus and strength of PPMs were characterized via three-point bend testing, while fracture toughness was determined with single edge notch bend testing. To analyze the adhesive performance of PPMs on asphalt, a shear adhesion testing approach was developed to measure the apparent debonding energy of PPM specimens on asphalt. The shear adhesion test was performed on asphalt road surfaces and cut surfaces to investigate the chemical and mechanical interfacial effects on adhesion. Two commercial thermoplastic PPMs with different mechanical properties were investigated to study how various factors directly affect the adhesion of PPMs on asphalt surfaces. Through mechanical tests, the relationships between the intrinsic materials properties and the mechanical performance of PPMs on asphalt were studied. A PPM material that had lower modulus and higher deformation energy exhibited greater adhesion performance on asphalt, especially when the PPM material was applied at higher asphalt surface temperatures on rough asphalt surfaces.

Performance comparison of carbon fiber reinforced polyaryletherketone and epoxy composites: Mechanical properties, failure modes, cryo‐thermal behavior, and finite element analysis

AbstractHigh‐performance thermoplastic composites are gaining attention as potential replacement for thermoset composites in high‐end structural applications owing to their superior fracture toughness and recyclability. In this study, polyaryletherketone (PAEK) and carbon fabric (CF) reinforced PAEK are compared with epoxy and epoxy‐CF composites. PAEK‐CF composites are prepared by film stacking method followed by compression molding while hand lay‐up technique was used for epoxy‐CF composites. PAEK and PAEK‐CF composites possess superior tensile properties, flexural strength and fracture toughness compared to those prepared from epoxy. The incorporation of CF improved the wear resistance in both PAEK and epoxy and PAEK‐CF exhibited the lowest wear rate. The investigation of interlaminar shear strength of the composites was conducted and the highest value observed for PAEK‐CF composite. Wear and fracture surface analysis suggested ductile failure for PAEK and PAEK‐CF composites and brittle failure in epoxy composites, as indicated by interfacial bonding/debonding and fiber pullout, at the fracture surface. Cryo‐thermal cycling effects on the tensile properties, fracture toughness and fracture surface morphology of the composites are studied. The failure behavior obtained from experimental studies was corroborated with finite element method‐based simulation models of fracture toughness response in single edge notch bend test using Abaqus/Explicit.

Study on 3D multi-performance composite films of Fe3O4 decorated CNTs/graphene oxide

In this work, three-dimensional (3D) Fe3O4 decorated CNTs/graphene oxide (Fe3O4-CNTs/GO) composite film was used to enhance glass fiber reinforced polymer (GFRP) resulting in three excellent performances of interlaminar toughening, resistance to temperature changes, and electromagnetic interference (EMI) shielding were all achieved. The end notch bending (ENF) test results showed that Fe3O4-CNTs/GO film enhanced GFRP was 60.51% and 79.64% higher than the baseline (GFRP without reinforcement film) after RT or temperature cycle treatment, while the GFRP of pure CNTs film was 21.79% and 26.34% higher than the baseline, respectively. The change in interlaminar toughness of Fe3O4-CNTs/GO samples by temperature cycle was also lower than that of the other two samples (Fe3O4-CNTs/GO film: 4.15%, pure CNTs film:11.15%, baseline: 14.35%). The average EMI shielding effectiveness of Fe3O4-CNTs/GO films with a thickness of only 0.052 mm was 25 dB, about 500% higher than the 5 dB of the control group (ordinary CNTs/Fe3O4/GO films, thickness 0.047 mm). Scanning electron microscopy (SEM) further confirmed the existence of the 3D frame structure and interlamellar strengthening interface of Fe3O4-CNTs/GO films.

Improvement of fracture toughness based on auxetic patterns fabricated by metallic extrusion in 3D printing

This study aims to evaluate the effect of auxetic patterns on the fracture toughness of 3D printed metallic specimens manufactured by metallic extrusion of 17-4PH stainless steel. When it is pulled in the horizontal direction, the auxetic material expands in the vertical axis. This occurs since it has a negative Poisson's ratio. In this work auxetic cell structures have been employed in fracture mechanics characterization of Single Edge Notch Bending SENB specimens in order to improve their fracture toughness dynamically during strain.SENB specimens were designed with different cell patterns for fracture toughness assessment. (i) Auxetic pattern at 0° parallel to the notch direction, (ii) at 90° perpendicular to the notch direction and (iii) a conventional honeycomb pattern is defined with equivalent cell density on the specimen surface. Three-point bending tests have been carried out to evaluate the fracture toughness of each specimen. The mechanical performance ratio of specimens was evaluated by dividing the absorbed energy till fracture over the specimen weight. The ratios were also compared to a solid specimen ratio taken as a reference in this study.The results show that all specimens with cell patterns absorb more strain energy than the solid specimen does. Although the solid specimen is the stiffest, both cell patterns (auxetic and honeycomb) have higher performance indices considering the important weight reduction. For around 35 % of reduction in the maximum measured load, the auxetic pattern at 0° can absorb up to 88% more energy compared to the solid specimen. This proves its capability of delaying the crack initiation and enhancing the fracture toughness.

Determination of fatigue crack growth in the near-threshold regime using small-scale specimens

A complete description of the experimental procedure for characterizing the intrinsic fatigue crack propagation threshold (ΔKth,eff) as well as the fatigue crack growth rate (FCGR) in the near-threshold regime using small-scale specimens is presented. A comparative study is carried out on the high strength steel S960QL considering different single edge notch bend (SENB) specimen geometries. On one hand, the reference dimensions of 6 mm thickness (B) and 19 mm width (W) are analysed and referred to as conventional specimens. On the other hand, small-scale specimens with B = 3 mm and W = 4 and 6 mm are also considered. Several loading configurations (3-, 4- and 8-point bending) are used and a load ratio R = 0.8 is applied to avoid crack closure effects. The direct current potential drop (DCPD) technique is used to monitor the crack length. The reduced dimensions of the small-scale specimens imply the necessity of implementing a modified testing procedure compared to the recommendations of current standards for the generation of FCGR data. The results show a good agreement between tests conducted on different specimen sizes, which opens new perspectives in the use of small-scale specimens for characterizing the fatigue crack growth properties in metallic materials. Recommendations and limitations of the procedure are provided and discussed.

Mode I fracture toughness of Carbon/glass hybrid comopsite

Mode I fracture toughness of carbon/ glass reinforced polyster hybrid composite was invesitigated expermrntally and numerically by using the cosmos)/m 2.6 finite element software (fms) by utulizing the hand laup techniqe)(HLU). The single edge notch bending (SENB) test was developed to evalute the mode l fracture toughness of carbon composites, glass composite and hybrid compodite materials at varuos fiber configurations. Scaning electron microscope (SEM) was used to examine the fracture surface of the hybrid composite material under the effect of mode l loading. the expermental result showed the maximum stress intensity (sif) factor 882mpa. mm1/2. obtained in the hybrid composite with stacking dequencess (c/g/g/c) during the mode l loading compared to other stacking sequences. this is attributed to the goid interfical between the carbon and glass fibers and matrix face. From the resukts, it was suggested that the expermental results is a goid a gremnent with the finite element modelling