Single-edge Notched Beam Test Research Articles

Study on the influencing factors of mechanical properties of anti-icing modified asphalt mortar

Accumulated snow and ice on road surface affect traffic operation. Anti-icing asphalt pavement is widely implemented as an active snow melting technology. However, there are few studies on anti-icing modified asphalt mortar mechanical properties and the effect of mortar materials on the interaction between modified asphalt and anti-icing filler. For this reason, this study investigated the mechanical properties of asphalt including rheological, high-temperature, fatigue and low-temperature properties through frequency and temperature scan, multiple stress creep recovery, linear amplitude scan, and single edge notched beam test. Based on this, the significant factors affecting asphalt mechanical properties were identified by analysis of variance. Subsequently, the Palierne-C-G* parameter was used to quantify the interaction between modified asphalt and anti-icing filler, and the effect of asphalt chemical structure on the interaction was revealed by Fourier Transform Infrared Spectroscopy (FTIR) test. The results indicated that the anti-icing filler significantly improved the high temperature and fatigue resistance of asphalt. Compared with SBS modified asphalt mortar, the mechanical properties of composite modified asphalt mortar were superior. The most significant factor affecting the mechanical properties of SBS modified asphalt mortar was modifier dosage, while the most significant factor affecting the composite modified asphalt mortar was crushed rubber dosage. The interaction showed a decreasing trend with the increase of frequency, while it appeared to increase and then decrease with the increase of temperature. The carbonyl functional group of asphalt correlated best with the interaction between asphalt and filler.

Automating the determination of low-temperature fracture resistance curves of normal and rubberized asphalt concrete in single-edge notched beam tests using convolutional neural networks

As materials undergo large-scale yielding or exhibit large sizes of fracture process zone in the crack tip region, multi-parameter fracture concepts should be employed to describe the complex crack-tip stress-strain fields. Fracture resistance curves (R-curves) are an established tool in characterizing the entire fracture process of such materials. However, for complex materials such as bituminous mixtures, the development of these curves is subject to experimental and computational intricacies. In this research, a framework is developed to automate the construction of R-curves for normal and rubberized asphalt concrete (AC) mixtures. AC mixtures are produced using PG58–22 and PG58–28 binders. Limestone and siliceous aggregates are used, and three binder contents are considered for the mixtures. Single-edge notched beam (SE(B)) fracture testing is conducted on AC beams with two different notch patterns. A convolutional neural network (CNN) model is developed and trained over 1260 test images with varying temperatures, notch geometries, and setups. The CNN model was used to detect the growing crack on the beam surface and each crack-detected image was sent to an image processing framework to measure the crack length. Crack extension increments were calculated and synchronized with test time and magnitude of load, load-line displacement, and cumulative fracture energy, and the R-curve could be constructed. A training accuracy of 0.91 was obtained for the model and a loss of below 0.10 as a result of a hyperparameter tuning indicating reliable classifications by the CNN architecture. The R-curves showed desirable agreement for control mixtures at temperatures of 0 °C and −15 °C. As the mixtures are rubberized, the R-curves showed favorable agreement in the crack blunting phase, transition zone, as well as the unstable propagation phase at −20 °C. Cohesive energy magnitudes were compared for the two methods with a Pearson coefficient of 0.81 while fracture rate and fracture energy magnitudes showed favorably close magnitudes with coefficients of 0.89 and 0.98 respectively.

Fracture toughness testing of metallic materials based on scratch tests

As a crucial parameter for determining a material's resistance to crack propagation, the convenient characterization of fracture toughness has attracted much attention. The scratch test is an alternate method for determining fracture toughness because it does not require notches or pre-existing cracks and only requires a minimal sample volume. In this study, the product of strength and elongation of materials is incorporated into a modified model based on the energy size effect law to calculate the fracture toughness of metallic materials using scratch tests. To validate the proposed model, scratch tests of DP800, 18CrNiMo7-6, 4140, and 4340 are performed to characterize their fracture toughness. The fracture toughness of these four metallic materials determined from scratch tests utilizing the proposed model, Akono's linear elastic fracture mechanics (LEFM) model, Akono's microscopic energetic size effect law (MESEL) model, Hubler's MESEL model, and Liu's MESEL model are compared with the results from a compact tensile test or single edge notched beam test. Our results indicate that our modified approach is applicable to metallic materials. The proposed model could be reduced to the linear elastic fracture mechanics model. This study offers an efficient way of characterizing the fracture toughness of materials using the scratch method.

Mechanical properties of N440/SiO2 composites with fugitive carbon interphases

ABSTRACT Mechanical properties of NextelTM 440 fiber-reinforced SiO2 composites containing fugitive carbon (FC) interphases were investigated. The three-point bending (TPB) test at room temperature indicated that FC interphases were crucial to the strength improvement. After employing FC interphases, the fiber/matrix bonding strength was weak enough for crack propagation, thus leading to the increase of flexural strength by about 2.1 times. The TPB test at high-temperature showed that the flexural strength decreased firstly and then increased as temperature increased, and the fracture mode changed from ductile to brittle. The lowest value of 92.3 ± 13.5 (MPa) was obtained at 1000°C. With the aid of the single edge notched beam test combined with the digital image correlation technique, cracks propagation process during fracture was well clarified.

Deformation and fracture behaviour of alumina-zirconia multi-material nanocomposites reinforced with graphene and carbon nanotubes

An effort to improve the low fracture toughness of monolithic alumina (Al2O3) ceramic demands microstructural manipulation with nanostructured materials such as zirconia (ZrO2), Graphene (GN) and Carbon Nanotubes (CNTs). Despite these attempts, the fundamental understanding of the mechanical properties and deformation behaviour of multiple combinations of these second-phase additives within the advanced Al2O3 structure are still being explored. In this respect, Al2O3-based nanocomposites reinforced with optimum amounts of ZrO2(10 wt%), GN(0.5 wt%) and CNTs(2 wt%) were evaluated via hot-pressing at 1600 °C, preceding colloidal mixing of the Al2O3 matrix and nanostructured additives. Mechanical properties such as fracture toughness (KIC) and bending strength (σf) measured using three-point bending techniques including single edge notched beam (SENB) test, and direct crack measurement (DCM) methods were calculated from the near-dense fabricated multi-material nanocomposites and benchmarked against the monolithic Al2O3 material under similar experimental conditions. From the conventional SENB test, the fracture toughness values increased by up to 60% on the addition of only 10 wt%ZrO2 to the monolithic Al2O3, whilst a drastic increase by up to 159% was achieved with the incorporation of both GN and CNTs within the Al2O3–ZrO2 structure, as compared to the monolithic Al2O3. The KIC values obtained from SENB tests were typically lower than the DCM method, but similar trend in the toughness behaviour were realized regardless. Bending strength of the prepared monolithic Al2O3 was also increased by up to 46% with the combined additions of ZrO2, GN and CNTs. Toughening and strengthening mechanisms including pull-outs by GN and CNTs, crack arrest and cack bridging were identified as the main source of enhancement in the mechanical properties of the multi-material nanocomposites. The addition of carbon additives also influenced monoclinic and tetragonal ZrO2 phase transformations, which also contributed to the overall mechanical behaviour of the Al2O3-10 wt%ZrO2 nanocomposites.

Use of Polyurethane Precursor–Based Modifier as an Eco-Friendly Approach to Improve Performance of Asphalt

With the rapid growth of traffic demands, the use of liquid chemical material instead of traditional modifier to prepare high-performance modified asphalt demonstrates dual values in environmental protection and performance improvement of pavement. The objective of this study is to assess the efficiency and reveal the modification mechanism of using a developed polyurethane precursor–based reactive modifier (PRM) in the preparation of polyurethane precursor–modified asphalt. The selected petroleum asphalts (60/80 pen grade) were modified at 1.5%, 2.5%, and 4% by weight. Samples of the base asphalt and PMA binders were characterized by dynamic shear rheometer, time sweep fatigue test, and single-edge notched beam tests. The modification mechanism was finally demonstrated by the fraction analysis, Fourier transform infrared spectroscopy, differential scanning calorimeter, atomic force microscopy, and fluorescence microscope. Owing to the presence of polar groups in neat asphalt, the use of PRM can be treated as a chemical method for the modification and it shows good compatibility with neat asphalt. The incorporation of PRM to the asphalt matrix can notably improve the high-temperature performance and fatigue resistance of asphalt. In addition, the PMA presents desirable low-temperature crack resistance and aging resistance. Considering the relatively low level of preparation temperature (145°C) and the huge improvement in high-temperature performance, the modification using PRM can be regarded as an environmentally friendly alternative for the production of polymer-modified asphalt, especially in high-temperature regions.

Study of mixed mode I/II cohesive zone models of different rank coals

The present work studies the Park–Paulino–Roesler (PPR) model, a unified potential-based cohesive zone model (CZM), for mixed mode I/II fractures in different rank coals, including weakly caking coals, fat coals and anthracite, by using disk-shaped compact tension (DC(T)) tests and punch-through shear (PTS) tests. The PTS experiments show that with the increase in coal rank, the initial shear stiffness and shear peak loads grow and the maximum tangential crack opening displacement (δt) decreases gradually. Additionally, the post-peak softening curve tends to have a linear shape, and the shear crack surface is rougher and more tortuous for the lower rank coals. The mode II fracture energy (Φt) was evaluated by calculating the area under the shear load–displacement curves. Φt is remarkably higher than mode I fracture energy (Φn) for the same coal rank, and the average value of Φt decreases from 145.54 J/m2 to 70.11 J/m2 as the coal rank of the specimens increases from weakly caking coals to anthracite. In order to verify the obtained PPR CZMs, mixed mode I/II single-edge notched beam (SENB) tests were performed and the experimental results are in good agreement with the numerical simulation. Moreover, we conducted SENB tests with different-size specimens, and the established PPR CZM model demonstrated its ability of describing the size effect of the mixed mode I/II fracture in coals.

A novel damage model in the peridynamics-based cohesive zone method (PD-CZM) for mixed mode fracture with its implicit implementation

Peridynamics (PD) becomes increasingly promising in computational fracture mechanics for its powerful ability to capture complex crack problems. Nevertheless, the PD applications are mainly limited to brittle fracture, and a robust PD model for predicting mixed mode fracture of quasi-brittle materials is still lacking. In this work, a novel damage model is proposed in the PD-CZM to accurately predict quasi-brittle failure under quasi-static mixed-mode loading, especially shear-dominated loading. In order to establish the damage criterion of quasi-brittle materials, the bond potential in bond based peridynamics (BBPD) is firstly separated into the dilatational part and deviatoric part. Instead of using existing bond stretch-based failure criterion, a new damage criterion obtained by combining bond stretch and dilatational bond potential is firstly proposed to determine the damage initiation. Also, the tension softening behavior of quasi-brittle materials is described in the damage model by a well-established degradation curve based on an energy-equivalence principle. Besides, to robustly solve the physical nonlinear characteristics, especially tension softening-induced snap-back phenomenon, the implicit implementation of the PD-CZM is performed with different implicit solution methods. Three challenging benchmarks are simulated to validate the proposed damage model, including Schlangen’s single-edge notched beam test, Nooru-Mohamed’s double edge-notched concrete specimen (DENS) test and Arrea and Ingraffea’s single notched shear beam test with severe snap-back behavior. Both the predicted crack paths and the load–displacement curves are in perfect agreement with the experimental observations and other numerical results, clearly demonstrating the validity of the proposed damage model and the robustness of the implicit implementation.

Hierarchically structured diamond composite with exceptional toughness.

The well known trade-off between hardness and toughness (resistance to fracture) makes simultaneous improvement of both properties challenging, especially in diamond. The hardness of diamond can be increased through nanostructuring strategies1,2, among which the formation of high-density nanoscale twins - crystalline regions related by symmetry - also toughens diamond2. In materials other than diamond, there are several other promising approaches to enhancing toughness in addition to nanotwinning3, such as bio-inspired laminated composite toughening4-7, transformation toughening8 and dual-phase toughening9, but there has been little research into such approaches in diamond. Here we report the structural characterization of a diamond composite hierarchically assembled with coherently interfaced diamond polytypes (different stacking sequences), interwoven nanotwins and interlocked nanograins. The architecture of the composite enhances toughness more than nanotwinning alone, without sacrificing hardness. Single-edge notched beam tests yield a toughness up to five times that of synthetic diamond10, even greater than that of magnesium alloys. When fracture occurs, a crack propagates through diamond nanotwins of the 3C (cubic) polytype along {111} planes, via a zigzag path. As the crack encounters regions of non-3C polytypes, its propagation is diffused into sinuous fractures, with local transformation into 3C diamond near the fracture surfaces. Both processes dissipate strain energy, thereby enhancing toughness. This work could prove useful in making superhard materials and engineering ceramics. By using structural architecture with synergetic effects of hardening and toughening, the trade-off between hardness and toughness may eventually be surmounted.

Investigations on fracture characteristics of geosynthetic reinforced asphalt concrete beams using single edge notch beam tests

Reflective cracking is a major cause for premature deterioration of asphalt pavements. Different varieties of geosynthetics are used at the interfaces of surface layers to control the reflective cracks. The significant factors influencing their efficiency are the flexural strength and interfacial bonding. Fracture energy that leads to development of cracks and their propagation can be investigated by single-edge notched beam (SENB) tests with sufficient accuracy. Double layered asphalt samples were extracted from pavement sections purposely built as part of this investigation for conducting quasi-static SENB tests. The goal of this paper is two-fold (a) to present a methodology for conducting SENB tests to measure the fracture properties of geosynthetic reinforced samples at temperatures of 10 °C, 20 °C and 30 °C and (b) evaluation of the flexural and the fracture characteristics of unreinforced and geosynthetic reinforced samples. The geosynthetic reinforcement did not show much improvement of the Asphalt Concrete (AC) in the pre-cracking phase but slowed down the crack propagation. The failure pattern of reinforced specimens has changed from quasi-brittle to ductile. An equation is proposed to predict the crack initiation force of SENB sample knowing the bond strength of the corresponding reinforced AC layers at their respective temperature.

Effect of Ti Addition on the Microstructure and Mechanical Properties of SiC Matrix Composites Infiltrated by Al⁻Si (10 wt.%)⁻xTi Alloy.

This paper proposes a simple reactive melt infiltration process to improve the mechanical properties of silicon carbide (SiC) ceramics. SiC matrix composites were infiltrated by Al–Si (10 wt.%)–xTi melts at 900 °C for 4 h. The effects of Ti addition on the microstructure and mechanical properties of the composites were investigated. The results showed that the three-point bending strength, fracture toughness (by single-edge notched beam test), and fracture toughness (by Vickers indentation method) of the SiC ceramics increased most by 34.3%, 48.5%, and 128.5%, respectively, following an infiltration with the Al–Si (10 wt.%)–Ti (15 wt.%) melt. A distinct white reaction layer mainly containing a Ti3Si(Al)C2 phase was formed on the surface of the composites infiltrated by Al alloys containing Ti. Ti–Al intermetallic compounds were scattered in the inner regions of the composites. With the increase in the Ti content (from 0 to 15 wt.%) in the Al alloy, the relative contents of Ti3Si(Al)C2 and Ti–Al intermetallic compounds increased. Compared with the fabricated composite infiltrated by an Al alloy without Ti, the fabricated composites infiltrated by Al alloys containing Ti showed improved overall mechanical properties owing to formation of higher relative content Ti3Si(Al)C2 phase and small amounts of Ti–Al intermetallic compounds.

Effect of fiber heat treatment on microstructure and mechanical properties of 2.5D T700 carbon fiber reinforced SiC composites

T700 carbon fibers were heat treated at 1300 °C and 1600 °C to investigate the effect on microstructure of pyrolytic carbon (PyC) interphase and mechanical properties of 2.5D T700 carbon fiber reinforced SiC (2.5D Cf/SiC) composites, and the untreated carbon fiber acts as a comparison. The flexural strength was measured using three-point bending test and the fracture toughness was evaluated by a single-edge notched beam test. Results show that heat treatment at 1300 °C leads to highest mechanical properties of 2.5D Cf/SiC composites, with the flexural strength in warp direction of 248.6 ± 12.3 MPa, the flexural strength in weft direction of 421.6 ± 15.1 MPa, and the fracture toughness of 18.7 ± 1.7 MPa · m1/2. Nevertheless, both the unheated and heat treatment at 1600 °C result in a decrease in mechanical properties. The microstructural investigations revealed that the bonding strength between the carbon fiber and PyC is best when the heat treatment of carbon fiber at 1300 °C.

Challenges in using the Disc-Shaped Compact Tension (DCT) test to determine role of asphalt mix design variables in cracking resistance at low temperatures

ABSTRACTThere have been many fracture tests – the Thermal Stress Restrained Specimen Test, the Single-Edge Notched Beam test, the Semi-Circular bend test, the Indirect Tensile Test and the Disc-Shaped Compact Tension (DCT) test – developed to understand thermal cracking in asphalt pavement. Among these tests, the DCT test is the most recent test method developed that has gained significant interest. This paper includes a laboratory study to measure the effect of different mixture design parameters on the DCT test results. The parameters include per cent binder replacement from recycled asphalt pavement, binder modification, low-temperature binder grade, oxidative ageing and mix design traffic level. To investigate the significance on the factors controlled, ANOVA and multi-linear regression analyses are used to show that only a few factors can be considered significant in terms of their effects on DCT parameters, and the significance of those factors could not explain the range in DCT response variables. Some of the trends in change in the DCT test responses with mixture ageing and some other factors are also found to be illogical. This paper does not offer solutions, but highlights some of the challenges experienced when applying the DCT test to performance specifications.

Inverse Estimation of Cohesive Fracture Properties of Asphalt Mixtures Using an Optimization Approach

Tensile cracking in asphalt pavements due to vehicular and thermal loads has become an experimental and numerical research focus in the asphalt materials community. Previous studies have used the discrete element method (DEM) to study asphalt concrete fracture. These studies used trial-and-error to obtain local fracture properties such that the DEM models approximate the experimental load-crack mouth opening displacement response. In the current study, we identify the cohesive fracture properties of asphalt mixtures via a nonlinear optimization method. The method encompasses a comparative investigation of displacement fields obtained using both digital image correlation (DIC) and heterogeneous DEM fracture simulations. The proposed method is applied to two standard fracture test geometries: the single-edge notched beam test, SE(B), under three-point bending, and the disk-shaped compact tension test, DC(T). For each test, the Subset Splitting DIC algorithm is used to determine the displacement field in a predefined region near the notch tip. Then, a given number of DEM simulations are performed on the same specimen. The DEM is used to simulate the fracture of asphalt concrete with a linear softening cohesive contact model, where fracture-related properties (e.g., maximum tensile force and maximum crack opening) are varied within a predefined range. The difference between DIC and DEM displacement fields for each set of fracture parameters is then computed and converted to a continuous function via multivariate Lagrange interpolation. Finally, we use a Newton-like optimization technique to minimize Lagrange multinomials, yielding a set of fracture parameters that minimizes the difference between the DEM and DIC displacement fields. The optimized set of fracture parameters from this nonlinear optimization procedure led to DEM results which are consistent with the experimental results for both SE(B) and DC(T) geometries.

Preparation and Properties of SiC/Si-B-C-N Ceramic Composites

Abstract：SiC/Si-B-C-N and SiC/SiC ceramic matrix composites were prepared through a combination of chemical vapor infiltration (CVI) and polymer impregnation pyrolysis process(PIP). The microscopic morphology and solid phase structure of the SiC/Si-B-C-N and SiC/SiC composites were investigated by SEM and XRD respectively. Moreover,the flexural strength and fracture toughness were measured using three point bending and single-edge notched beam test. Results showed that the formation of crystalline phases transformation was restrained by introduce BN into matrix phase, which might improve the stability of ceramic matrix composites. Furthermore, the flexural strength and fracture toughness of ceramic matrix composites increased to a maximum of 367 MPa and 26.81 MPa·m1/2 with the 30% PBN weight ratios which might be mainly caused by crack arresting, crack deflecting, micro cracks and fiber pullout.

Forward and Inverse Analysis of Concrete Fracture Using the Disk-Shaped Compact Tension Test

Abstract A new concrete fracture geometry is presented, which can quantify multiple fracture properties from a single specimen test. The disk-shaped compact tension (DCT) geometry allows specimens to be fabricated from laboratory cylinders or field cores. The DCT fracture test characterizes the concrete's critical stress intensity factor, KIC, critical crack-tip opening displacement, CTODc, and initial fracture energy, Gf, as well as the specimen-dependent total fracture energy, GF. The DCT-based fracture properties have the same experimental variation as the single-edge notched beam test. The experimentally derived fracture parameters were implemented into a cohesive zone model, which enabled estimation of concrete tensile strength from field-extracted cores.

Three-Dimensional Discrete Element Modeling of Crack Development in Epoxy Asphalt Concrete

Abstract Cracking in epoxy asphalt concrete (EAC) used for a steel bridge wearing course has always been a major cause of structural and functional deterioration of this material, particularly in cold climate. Therefore, it is important to understand the complex fracture behavior of this heterogeneous mixture, which is composed of irregularly shaped and randomly distributed aggregates surrounded by asphalt mastics. A three-dimensional (3D) fracture model independent of laboratory, based on the discrete element method (DEM), is reconstructed using a randomly generating algorithm to investigate the fracture behavior. A bilinear cohesive-softening model is implemented into the DEM framework to simulate the crack initiation and propagation in EAC. Several experimental tests are performed to obtain input parameters of materials for numerical models. The simulation results of a single-edge notched beam test agree well with experimental results and accurately capture the stress distribution and development of fracture zone. The modeling technique herein provides insight into the progressive cracking process; 3D visualization of crack trajectories also demonstrates the influence of heterogeneity on crack path. The 3D user-defined microstructural DEM fracture model is capable of giving a realistic cracking process of quasi-brittle materials such as EAC and can help us better understand various fracture mechanisms through numerical simulations.

Integrated Experimental-Numerical Approach for Estimating Asphalt Mixture Induction Healing Level through Discrete Element Modeling of a Single-Edge Notched Beam Test

AbstractThe induction healing effects have been experimentally investigated through the cyclic beam fracture and healing testing of asphalt mixture samples with conductive steel wool fibers. This study aims to investigate the healing level of asphalt mixture through the integrated work of laboratory experiment and numerical simulation. Nine single-edge notched beam (SENB) samples containing steel fibers were prepared and used for the laboratory fracture test. Afterward, three divided groups of fractured samples were subjected to the induction healing at controlled temperatures of 60°C, 80°C, and 100°C, respectively. Then the reloading fracture test was conducted with three groups of samples to measure the fracture strength recovery ratio (FSRR) after induction-healing process, which is defined as the ratio of the recovered peak load to the original peak load. The discrete element method (DEM) was utilized to simulate the beam fracture process. A fracture toughness-based bond healing model was used to simu...

Mechanical properties and toughening mechanism of WC-doped ZrB2–ZrSi2 ceramic composites by hot pressing

WC-doped ZrB2–ZrSi2 ceramic composites were fabricated by hot pressing at temperatures ranging from 1450°C to 1550°C. The influence of ZrSi2 content on the mechanical properties of the composites was investigated by means of three point bending test and single edge notched-beam test, respectively. The microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The results revealed that: (i) the highest relative density was 99.5% for the composite fabricated at 1550°C; (ii) the doping of WC refined the grain size and led to an anisotropic grain growth which was evidenced by the occurrence of elongated grains; (iii) the highest strength and fracture toughness were 585MPa and 6.87MPam1/2, respectively; (iv) the main toughening mechanism was considered as the pull out of elongated grains and the deflection of cracks.

Semi-circular notched beam testing procedure for hot mixture asphalt

The purpose of this study was to facilitate and improve the methodology used for hot mixture asphalt fracture evaluation and to establish a procedure to overcome the difficulty of preparation of hot mixture asphalt beam samples for fracture testing. This research investigated and compared the stress intensity factor (KIC) determined by two test set-ups: the semi-circular notched beam and the single edge notched beam tests. In addition, the temperature effect was evaluated by the determination of KIC at different temperatures. Two Superpave mixtures were used for experimental verifications. Results illustrated that there was no significant difference between KIC determined by semi-circular notched beam and single edge notched beam tests within the acceptable statistical margin of error. Finite-element and discrete-element models were created to aid in the verification of the results from the laboratory tests. Further, the evaluation of KIC by semi-circular notched beam at different temperatures showed a similar pattern for all tested mixtures. It was observed that the linear elastic fracture mechanics theory restrictions were not violated when determining KIC for all testing conditions. Overall results suggested that the semi-circular notched beam test can be used for fracture evaluation of hot mixture asphalt, as a screening tool for weak mixtures due to its simplicity and repeatability.