Notched Bending Tests Research Articles

Interlaminar performance of three nanomaterials film enhanced glass fiber reinforced polymer

The carbon nanotube (CNT) and graphene oxide are widely applied in Glass Fiber Reinforced Polymer (GFRP) to enhance interlaminar performance, even though they have an extremely expensive price. Herein, we provide a novel interlaminar toughening material: carbon black, which has a cheap price and good interlaminar properties. The relationship between different amounts of three nanomaterials and toughening efficiency is obtained through experiments (end notch bending (ENF) test) and the curves between different amounts and prices are revealed by the investigation. Moreover, a mathematical model of interlaminar performance, material consumption, and price is established, which can provide researchers with accurate, efficient, and inexpensive predictions in different application environments. On the other hand, a simple and efficient spraying method for making reinforcement layers is adopted in this research and we analyzed the microstructure strengthening mechanism of three nanomaterials by scanning electron microscopy (SEM).

Influence of layering sequence on performance of jute/wool epoxy hybrid composites: a comparative study with automotive plastic

Natural fibres such as Jute and Wool are increasingly being used in fibre reinforced polymer composites, hence progressively supplanting synthetic fibres. Combining these two unique natural fibers would improve the performance of composites used in secondary structural applications. This study is intended to investigate the effects of Jute and Wool fiber arrangement on mechanical properties in an epoxy matrix. In order to achieve this, hand layup was employed to fabricate composite laminates consisting of four layered fabric layers stacked in sequences, as Jute/Wool/Wool/Jute (JW1), Wool/Jute/Jute/Wool (JW2), Jute/Wool/Jute/Wool (JW3), and Jute/Jute/Wool/Wool (JW4). Effect of these stacking sequences on the properties of Natural Fibre Hybrid Composites (NFHCs) was evaluated by conducting a series of standardized tests such as Flexural, Interlaminar Shear Strength (ILSS), Impact and Single End Notch Bend (SENB) tests, as per ASTM standards. On the other hand an automobile interior thermoplastic material was evaluated for different mechanical properties and compared with hybrid Jute-Wool composite. Experimental results showed that the JW1 composite, exhibited superior mechanical properties because it has tailored with a Wool fabric at the core and Jute fabric on its outer surface. Hence, JW1 had a remarkable tensile strength of 40 MPa, a maximum flexural strength of 99 MPa and extremely high interlaminar shear strength (ILSS) of 3.09 MPa. In addition to this, JW1 also had high fracture toughness, measuring around 72 M P a m 1 /2, and impressive impact strength of 85 J/m2. Furthermore, scanning electron microscope (SEM) photo images confirmed that the presence of strong bonding between the fibres and matrix in JW1 composite exhibited and overall improvement of mechanical performance by 82% when compared with other combinations (JW2, JW3, and JW4) including automotive plastics.

Enhanced damage tolerance and fracture toughness of lightweight carbon-Kevlar fiber hybrid laminate

Low damage tolerance and residual strength are the main drawbacks of carbon fiber composite laminates that limit their application in many lightweight structures. This study demonstrates the exceptional damage tolerance and high fracture toughness of carbon-Kevlar hybrid laminate, where Kevlar plies are placed between two carbon fiber face sheets. Flexural strength after damage and mode I translaminar fracture toughness of carbon and Kevlar and the hybrid laminates were evaluated using three-point bending and single-edge notched bending tests, respectively. The damage mechanisms in the three configurations were investigated using micro-computed tomography and correlated with their mechanical responses. The results showed that the hybrid laminate could sustain 70% of the laminate strength after fiber damage occurs and can sustain the same strength for large strains, unlike carbon and Kevlar fiber laminates, where they both lose their mechanical integrity after fiber breakage. Moreover, this laminate showed 200% and 170% larger specific absorbed energy than carbon and Kevlar laminates, respectively. The improvement can be justified by the propagation of fiber breakage at three different positions in the Kevlar core and the delamination at the carbon-Kevlar interface that allowed larger energy dissipation during fracture. Additionally, it showed 21% and 42.7% larger absolute and specific fracture toughness, respectively, than the carbon fiber laminate.

Experimental Study of the Physical and Mechanical Properties of Cement‐Based Composite Reinforced With Macro‐/Microfibers: Case of Rhecktophyllum camerunense and Triumfetta pentandra

Plant fibers have the ability to bridge crack propagation on a microscopic scale for microfibers and on a macroscopic scale for macrofibers. Therefore, the use of two or more fiber types in an appropriate combination can potentially improve the overall properties of the cement composite as well as promote green construction. The hybrid composite was cast using random orientation with two fibers: Rhecktophyllum camerunense as macrofiber and Triumfetta pentandra as microfiber. Cement mortar matrices were reinforced with a constant microfiber length of 1 mm and three different macrofiber lengths of 1.5, 3, and 6 mm at varying fiber contents of 1%, 1.5%, and 2.5% wt. The physical characteristics of the composite were assessed by porosity, density, and water absorption. Mechanically, three‐point bending tests and single‐edge notch bending (SENB) tests were performed after 7 and 14 days of curing. Mode I fracture behavior (KIC) and modulus of rupture (MOR) were calculated as per formulation. Physical experimental results reveal that there is a correlation between the rate of water absorption, porosity, density, and that of the fiber loading and length in the composite. Mechanically, the developed material presented a multiple cracking behavior under bending. There was a decrease in MOR and fracture toughness values with a decrease in macrofiber content in the hybrid composite. They both presented an increase in value with an increase in fiber content and fiber length. The composites reinforced with both fibers presented higher values of MOR than the unreinforced due to the powerful interfacial bond between the fibers and the cement matrix. The unreinforced composites had the least MOR and fracture toughness values of 0.442 MPa and 694,000 N.m1.5, respectively, showing that they are very reactive to faults at low stress levels.

Fracture of all‐oxide ceramic composites: Crack path analysis by surface strain monitoring

AbstractCrack propagation in ceramic matrix composites is very difficult to observeand to quantify. To investigate crack formation in all‐oxide ceramic composites, single edge notched bending tests were performed including loading‐unloading cycles and online monitoring of surface deformation using digital image correlation. The crack length was calculated by the compliance method with the crack opening displacement determined optically using digital image correlation. Obtained crack length values were found to be too small considering the sample geometry. Secondly, surface strain monitoring was used to investigate the crack growth. Analysis of cyclic force‐crack opening displacement curves and the results from strain monitoring indicated no major crack growth for loads below maximum force but still a moderately decay of force after onset of cracking. Graphical analysis of the surfaces of broken samples showed crack flank lengths ranging from 3 to 6 mm. Due to highly individual crack deflection mechanisms throughout the thickness of the oxide ceramic composites, deviations between front and back of specimens are found. The results demonstrate the necessity to use individual crack length measurements of each specimen for quantitative fracture mechanical evaluation. Strain monitoring during testing was shown to be a valuable tool for online crack path investigation.

Anisotropic and elastoplastic mode‐I fracture toughnesses of three additively manufactured polymers fabricated via material extrusion and powder bed fusion

AbstractTwo types of additive manufacturing (AM) techniques, fused filament fabrication (FFF) and selective laser sintering (SLS), were employed to fabricate specimens from three widely used AM polymers: polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyamide (PA): the first two using FFF and PA using SLS. The single‐edge notch bending (SENB) test was employed to measure the mode‐I fracture toughnesses of bulk and AM specimens in three directions relative to the printing direction. Unlike their bulk counterparts, AM polymers exhibited anisotropic fracture toughness. The degree of anisotropy in FFF‐PLA was much larger than FFF‐ABS and SLS‐PA. The smallest fracture toughness value for each AM polymer was achieved along the transverse printing direction. Different AM techniques affect fracture toughness differently. For instance, FFF is shown to increase PLA's plastic deformation, while SLS reduces PA's ductility. The decrease in fracture toughness is consistently observed when transitioning from bulk polymers to AM ones, reaching as much as 75%. This study provides insights into the fracture toughness of AM parts made via popular plastics, which are crucial for designing structural parts using FFF and SLS processes.

Impact-dynamic properties of aromatic hyperbranched polyester/RTM6 epoxy nanocomposites

Present study investigates the influence of aromatic hyperbranched polyester (AHBP) nanofillers on the impact-dynamic properties of RTM6 epoxy. The strain rate dependence of the energy absorption capacity of neat RTM6 epoxy and RTM6 nanocomposites with filler weight ratios of 0.1%, 1%, and 5% was determined through compression testing. Additionally, static and dynamic tensile tests were performed on these materials. Universal testing machines were used for the quasi-static tests, split Hopkinson bar setups for the high-strain rate experiments. Furthermore, dynamic single-edge notch bending (SENB) tests were conducted to measure fracture toughness using an adapted split Hopkinson compression bar setup. In addition to global deformation measurements, full-field deformation measurements were also performed in all experiments using the digital image correlation (DIC) technique. The results indicate that the energy absorption capacity, tensile strength, fracture strain, and toughness are significantly influenced by both strain rate and filler content of the RTM6 epoxy.

Flexural and fracture behavior of additively manufactured carbon fiber reinforced polymer composites with bioinspired Bouligand meso-structures

Carbon fiber reinforced polymer (CFRP) composites are strong and lightweight materials extensively used across aerospace, automotive, and construction industries. Bioinspired designs such as Bouligand structures have the potential to improve the mechanical properties of CFRP composites. In this study, we examine the effects of the single and double Bouligand meso-structures with varying twist angles on the flexural and fracture properties of additively manufactured continuous CFRP composites. 3-point flexural tests are conducted to characterize the flexural properties such as flexural modulus, strength, and energy absorption. Single edge notch bend (SENB) tests are performed to quantitively characterize the mode I fracture toughness and effective fracture energy. The elasto-plastic fracture theory is used to quantify the contributions of elastic and plastic energies to the effective fracture energy. Experimental results indicate that twist angles significantly affect the flexural behavior of CFRP composites. The Bouligand meso-structures with a twist angle of 10° increase the flexural strain energy absorption by 2-3 times. The single and double Bouligand layup configurations with the same twist angle result in different flexural properties. In addition, the twist angle affects the magnitude of fracture toughness. A twist angle of 10° results in an improvement of up to 60% in fracture energy dissipation compared to the quasi-isotropic meso-structure. The single and double Bouligand meso-structures with the same twist angle exhibit almost the same fracture toughness and absorbed fracture energy. The Bouligand meso-structures do not increase fracture toughness and elastic fracture energy for crack initiation compared to the quasi-isotropic meso-structure.

Study on Numerical Simulation Method of Fracture Behavior of Pipeline Girth Weld

Abstract The failure accidents in girth weld of pipelines occur frequently due to the combination of internal defects and external loads. However, the research on the fracture behavior of girth weld defects is relatively poor at present. To solve this problem, the cracking behavior and strain evolution law of the inner wall defects of the pipe girth weld are studied in combination with full-scale tests (FST). The constitutive and Gurson-Tvergaard-Needleman damage parameters of the pipe base metal zone, weld zone and heat-affected zone (HAZ) are calibrated through the small punch test (SPT) and single edge notch bending (SENB) test. On this basis, the welded pipe model with inner wall defects is established, and a numerical simulation method for dynamic fracture behavior based on damage mechanics is formed. The numerical simulation method is verified by FST data and theoretical calculation. The results show that the numerical results are consistent with the FST and theoretical calculation in the elastic stage, plastic stage, and fracture stage, and the error is within 10%. The novel numerical simulation method is provided as a means for the fracture behavior research of pipeline girth weld.

Temperature-dependent mechanical properties and fracture behavior of directionally solidified Ti47Al2Cr2Nb alloy

The influence of temperature on mechanical properties and fracture behavior of directionally solidified (DS) Ti47Al2Cr2Nb alloy was investigated in detail. Tensile tests and single-edge notched bending tests were performed in the temperature range of room temperature (≈25 °C) to 900 °C. The results revealed that both the yield strength and tensile strength of DS alloy specimens were insensitive to temperature until 850 °C. The yield strength and tensile strength at room temperature were found to be 500 MPa and 610 MPa, respectively, which were close to those at 850 °C (i.e., 534 MPa and 575 MPa). The ductility increased with the increase in temperature and the ductile-brittle transition (elongation >5%) occurred in the temperature range of 700–800 °C. Furthermore, the fracture toughness initially increased with the increase in temperature and reached the maximum value of 45 MPa m1/2 at 850 °C, followed by a decrease. It is worth emphasizing that the DS Ti47Al2Cr2Nb alloy exhibited a brittle trans-lamellar fracture at room temperature, which was similar to cleavage fracture. On the other hand, the fracture at high temperatures was influenced by the propagation and coalescence of microcracks at the lamellar interface, similar to micro-void accumulation fracture.

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.

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.

Study of extended and generalised finite element methods in 2D and 3D applied to a single edge notched bending test

Study of extended and generalised finite element methods in 2D and 3D applied to a single edge notched bending test

Fracture toughness evaluation of zeolite/polyurethane-filled woven panels

Recently, due to their extraordinary strength-to-weight ratio and multi-functional applications, three-dimensional woven fiberglass sandwich structures have become a well-received topic by researchers and manufacturers. Nevertheless, using light and foam absorber materials as injected fillers within sandwich cores can improve their overall mechanical performance and, in particular, their fracture toughness behavior. This study evaluates the fracture toughness of three-dimensional woven fiberglass sandwich panels filled with natural nano-structured zeolite/polyurethane foams injected between their parallel panels. The Single-Edge Notched Bend test was carried out to understand the effect of the injected foam on the mode-I fracture toughness response. It is demonstrated that the polyurethane foam reinforced with natural nano-structured zeolite particles highly improved the fracture toughness of sandwich core panels. It was found that the presence of vertical glass yarns within the sandwich panel gallery resulted in a significantly higher toughness compared with typical sandwich panels of no reinforcing vertical columns confirmed by the crack propagation and observed failure mode. The SEM and EDX analyses were used to better understand the correlations amongst the specimen morphology, the cracks behavior, and the toughness exhibited by the fabricated specimens.

Determination and influential factors of fracture toughness in unidirectional laminated bamboo-composite using double cantilever beams and single-edge notched bend tests

This paper studied two testing methods for determining the matrix-dominate fracture toughness in the unidirectional bamboo laminate panels, using double cantilever beam tests and single-edge notched bend tests. For single-edge notched bend tests, an isotropic solution was proposed to calculate the fracture toughness in which only the load-CMOD curve is required. In this isotropic solution, when calculating the energy release rate G Ic by G Ic = (K Ic ) 2 /E, the modulus of elasticity E can be directly obtained from the experimental load-CMOD curves, the pre-determination of Young’s modulus E x , E y , shear modulus G xy and Poisson’s ratio υ xy , υ xy is unnecessary for orthotropic materials. The results of modulus of elasticity E, the stress intensity factor K Ic , and energy release rate G Ic using the isotropic solution were compared to those using an orthotropic solution; it revealed that the isotropic solution could be well applied to unidirectional bamboo laminate panels with errors under 2.7%. The isotropic solution for single-edge notched bend tests was also verified by comparing the results to those obtained from double cantilever beam tests; it turned out that the energy release rate values determined by the two testing methods agreed well with each other. Moreover, the influence of initial notch width, initial notch to depth, and specimen depth on the fracture toughness was investigated to put forward a practical testing method to obtain the size-independent fracture toughness of unidirectional bamboo laminate panels by single-edge notched bend specimens.

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.

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.

Flexural tests and analysis of notched specimens of glass fiber reinforced composite

Fracture of notched Specimens of laminar glass fiber reinforced composite is quasi-brittle and with noticeable delamination crack growth around the notch tip, as indicated by the non-linear load–deflection curve close to the peak fracture load. In order to analyze the fracture performance of the composite with highly heterogeneous and anisotropic microstructures, the boundary effect model (BEM) considering the composite layered structures and damage along and perpendicular to the notch was adopted in this study. Around 90 notched three-point bending specimens with the span from 40 to 90 mm, plate thickness around 10 mm, the initial notch depth from 3 to 6 mm were tested and the maximum load Pmax values were recorded. The average fiber ply or layer thickness Cch was the characteristic microstructure modelled by BEM for both the crack-tip damage zone length (crack-bridging) and width (delamination). Both the tensile strength ft and fracture toughness KIC were determined from the notched bending tests. Direct tensile tests were also conducted and the measured tensile strength ft was close to the measurement from the three-point bending tests with the relative error < 6 %.