Single Edge Notched Bending Tests Research Articles

The Influence of the Rolling Direction on the Mechanical Properties of the Al-Alloy EN AW-5454-D

A complementary characterisation of the Al-alloy EN AW-5454 was carried out, intended for obtaining the laser hybrid welding parameters of subassemblies in the automotive industry. The investigation included a microstructural examination and the determination of the alloy’s properties using several analytical methods (HV5 hardness measurement, tensile test, Charpy impact toughness, fracture mechanics analysis). Samples were prepared in the longitudinal and transverse directions of a cold-rolled sheet of EN AW-5454 with thicknesses of 3.5 mm and 4 mm. The measured hardness on the thinner sheet was 5% higher than on the thicker sheet. The tensile and yield strength were nominal, while the elongations were smaller by 2.2–3.2% for the longitudinal samples and by 2.7–13.7% for the transverse samples. The smaller deviations from the nominal values are for the thinner sheet metal. A precise topographical analysis showed the brittle fractures of the samples. The Charpy impact toughness results on the thicker plate showed a 20% greater work needed to break it in the longitudinal direction than in the transverse direction. With the thinner sheet metal, 40% greater work was needed. SEM (scanning electron microscope) analysis has shown that the intermetallic Al6(Mn,Fe) particles in the longitudinal samples were mostly intact, with evidence of tough areas on the upper part of the fracture, indicating a better toughness than the specimens in the transverse direction. More crushed intermetallic particles were observed at the fractures of the transverse samples, and their distribution appeared to be more oriented in the direction of rolling. Fracture mechanics SENB (single edge notch bending) tests and their analysis showed that the resistance of the material to crack propagation in the longitudinal sample was about 50% greater than that in the transverse sample. SEM analysis of the fractures showed that the state of the intermetallic particles in the fracture mechanics testing and the fracture mechanism differed from the one in the Charpy fractures.

Comparison of Mode I fracture toughness of an elastic and an elastoplastic methyl methacrylate polymer as measured by SENB and DCDC tests

An elastic and an elastoplastic methyl methacrylate polymer, both in the glassy state, have been submitted to mode I fracture characterization with two different tests, the single edge notch bending (SENB) and the double cleavage drilled compression (DCDC) tests. The elastic material toughness was simply assessed by the linear elastic fracture mechanics analysis. For the elastoplastic material, the J-integral was computed when the strain fields were available. Moreover, numerical analyses were carried out using finite element simulations with a phase-field damage approach, providing comparison when the J-integral had been calculated and estimate otherwise, of the critical energy release rate. For each material, as well as for each test, the values of the critical energy release rate that have been estimated here, are in good agreement with the literature. More interestingly, for the same material, both tests provide with very different estimates of this material parameter, leaving engineers uncertain on which test to choose to assess the material toughness in crack opening mode.

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.

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.

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.

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.

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.

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.

Study the effect of fracture toughness on hybrid composite for automotive application

Fiber-reinforced plastics (FRP) possess good fatigue resistance, high stiffness, and resistance for corrosion. These mechanical properties helps in vast application in industries such as marine, automotive, aerospace, and bio-medical. Different types of fibers materials have been incorporated into a various matrix which has led to the development of hybrid composites. These hybrid composite that containing two or more types of fiber proves to be most advantageous as one type of fiber could supplement the properties where other fibers fail. The main objectives of this paper are the fabrication of the hybrid composites and study the variation of the fracture toughness. For the fracture toughness different tests like single edge-notched bending (SENB) test experimentation were carried out. In this study fabricated hybrid composite using hand layup technique with varying fiber matrix composition is machined using water jet machining as per ASTM standard. An experimental study for fracture toughness of hybrid composites was carried out as per SENB test method. The main intention of this research was to explore the variation of properties of composite material for fracture toughness which will be suitable to use in automotive applications.

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.

Low-temperature fracture characteristics of asphalt mixtures using the eccentric single-edge notched bend test: A 3D discrete element study

The single-edge notched bend (SENB) test has been widely employed to characterize the low-temperature fracture characteristics of asphalt mixtures. In this test, the pre-fabricated notch is typically fixed at the beam midline, but variation in its location has a significant impact on the resulted crack resistance. This study utilized the three-dimensional discrete element method (DEM) and evaluated the 16 SENB test configurations with different notch offset levels (i.e., the eccentric SENB test). The simulation results are interpreted using macroscopic parameters including crack morphology, main crack deflection angle, mixed-mode parameter and effective mixed-mode fracture toughness, and also from the mesoscopic perspective (crack propagation mechanism and contact fracture rule). The macroscopic analysis shows that the crack morphology can be categorized into three types: pre-notch bending crack, mixed-mode crack, and bottom bending crack, and that the main crack deflection angle is affected by the stress concentration at the crack tip caused by the top load and beam bending deformation. Moreover, the low-temperature crack resistance is affected by the degree of the beam bending deformation and microcrack damage evolution. The load mixing degree is mainly affected by shear stresses for the pre-notched bending crack and by tensile stresses for the mixed-mode crack. At the meso-level, the DEM model provides a realistic visualization of the crack propagation process and accurately captures the mesoscopic contact failure mechanism in the crack propagation process using crack fragments. This study provides a new approach to understand better various fracture mechanisms of asphalt pavement from both the macro- and meso-perspectives.

Interfacial and Interlaminar Shear Strength of Unidirectional Viscose Fibre-Reinforced Epoxy Composites—an Overview of the Comparability of Results Obtained by Different Test Methods

In this study, the apparent interfacial and interlaminar shear strength (IFSS and ILSS) of single fibres and unidirectional (UD) viscose fibre-reinforced epoxy composites were characterised using different test methods. Microbond and pull-out tests were used to analyse the IFSS of single fibres embedded in epoxy and the transverse tensile test was applied to measure the IFSS of UD fibre-reinforced composites. The short beam shear test, single edge notched bending test (SENB), double-notched tensile test and double-notched compression test were applied to characterise the ILSS. The composites were produced from continuous tows with fibre mass fractions of 20%, 30% and 40% and fibres of different fineness (1.7, 3.3 and 28.0 dtex). The results showed that the different test procedures led to different trends of ILSS depending on the fibre mass fraction and fibre fineness used. The transverse tensile test revealed that the IFSS decreased with increasing fibre mass fraction and fibre diameter. A different trend was found with the short beam shear test and the SENB test for the ILSS. Here, higher values were detected with increasing fibre mass content, and the influence of the fineness was less noticeable. The double-notched shear tests (tensile and compression) showed a different trend: the ILSS increased with increasing fibre mass fraction from 20% to 30%. With a further increase to 40%, the ILSS tend to decrease slightly. An influence of the fibre fineness on the ILSS could not be statistically proven. The different trends of the test methods are attributed to the constitution of the composite and the different load application caused by the test procedures.

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.