Initiation Fracture Toughness Research Articles

Understanding the interface fracture mechanism by composite BFPMPC mortar and cement concrete bending beam

This study aims to utilize basalt fiber-reinforced polymer-modified magnesium phosphate cement (BFPMPC) mortar as an overlay for rapidly repairing surface defects such as raveling and delamination on Portland cement concrete (PCC) pavements, thereby swiftly restoring traffic flow and enhancing pavement service durability. Initially, double layered three-point bending fracture (DLTPB) tests were conducted on composite BFPMPC and PCC specimen with different predetermined crack lengths. The flexural strength was measured, fracture parameters were obtained based on the double-K fracture criterion, and crack propagation paths were determined using digital image correlation (DIC) methods. Subsequently, the fracture behavior of the composite beam was predicted by boundary effect model, and the interface microstructure between BFPMPC and PCC was characterized using nanoindentation, nano-scratch, and SEM/EDS techniques. Finally, by analyzing the fracture characteristics of the composite specimens, the crack propagation model was established and validated by finite element analysis (FEA). The results indicated that BFPMPC mortar overlay can enhance the flexural strength of composite structure. The unstable fracture toughness, cohesive fracture toughness, and fracture energy decreased with increase of crack length-to-height ratio (a0/D), while the initiation fracture toughness increased with increase of a0/D. DIC measurements provided insights into the morphology of the crack tip and the length of the fracture process zone (FPZ). The boundary effect model predictions aligned with the fracture characteristics of the specimens, which were controlled by nonlinear fracture criteria. Nanoindentation tests revealed that the mechanical properties of the interface are influenced by multiple sub-interfaces, with the elastic modulus relationship being ITZ-4 > ITZ-2 > ITZ-3 > ITZ-1. Further analysis of scratch hardness and scratch fracture toughness confirmed that the BFPMPC-PCC interface exhibited high fracture toughness, which was crucial for improving structural resistance to fracture. SEM/EDS observations revealed significant cracks at the interface between BFPMPC and ordinary Portland cement (OPC), while cracks between BFPMPC and coarse aggregates were smaller. Subsequently, the fracture analysis model for composite specimens was proposed to finely reveal interface fracture failure, and the FEA results exhibited a high degree of consistency with experimental results.

A Methodology to Assess Directional and Spatial Variations of Tensile and Fracture Properties in Fabricated Nuclear Components

AbstractIn the present study, directional and spatial variations in the mechanical properties are calculated in two nuclear-grade materials. In practice, multiple ASTM standard specimens are tested to measure mechanical properties of any material. The variations obtained in the properties during the tests are generally neglected assuming such variations are due to experimental uncertainties. However, such variations may indicate some degree of anisotropy and spatial inhomogeneity in the material due to component fabrication. In the present study, multiple miniaturized tensile specimens are tested. These specimen materials are taken across the thickness and at different geometrical locations in the two manufactured nuclear-grade components. The experimental load versus displacement data of all the specimens are then used to evaluate stress-strain data and cohesive zone parameters. These parameters are determined for each tested specimen separately to gather variations over the geometries of the components. Subsequently, TPB specimens are analyzed employing these parameters to calculate variations in fracture initiation toughness over the geometry. The key findings of the present work include higher strengths in circumferential direction in comparison to the longitudinal direction for SA333 Gr6 steel. A new equation is developed to correlate the material toughness with the fracture toughness with a proportionality constant of 2.7778 for low-alloy carbon steels. The study showed that directional and spatial variations in Jini are less pronounced in 20MnMoNi55 compared to SA333Gr6 materials. This finding is crucial for safety analyses in nuclear components and indicates that this methodology can be applied more widely across different materials.

Insights into the fracture properties of recycled ceramic and rubber composite cement-based materials: Fracture mechanics, acoustic emission, and digital image correlation

Recycling plays a pivotal role in construction waste management, offering a path toward sustainability for the industry. Although waste ceramics can compensate for the mechanical properties of rubberized cement-based materials, the smooth glaze surface of waste ceramics increases the risk of brittle failure. This study investigated the effect of ceramic waste aggregate (CWA) on the fracture properties of rubberized mortar through the three-point bending experiment. The fracture parameters were calculated using the Double-K fracture criterion. Simultaneously, acoustic emission (AE) and digital image correlation (DIC) technologies were used to explore the fracture damage mechanism and the crack evolution process. The results indicate that the integration of 15 % and 45 % CWA significantly enhances both initiation (KICini) and unstable (KICun) fracture toughness, whereas incorporating 90 % CWA leads to a 16.8 % and 8.2 % decrease in (KICini)and (KICun), respectively. The fracture energy (GF) of rubberized mortar exhibits a continuous decline as a function of increasing CWA substitution rates. Furthermore, GMM-based RA-AF analysis elucidates a positive correlation between CWA content and tensile crack proportion in specimens. When the CWA content reaches 90 %, the proportion of tensile cracks is quantified at 29.83 %, surpassing that in standard mortar. Crack tip opening displacement (CTOD) at 0.5post-Pmax for specimens with 15 %, 45 %, and 90 % CWA substitution reveal improvements of 49.1 % and 17.2 %, and a decrease of 23.3 %, respectively, compared to standard mortar, indicating that 15 % and 45 % CWA effectively preserve the ductility of rubberized mortar. Elevated CWA substitution leads to an amplified strain localization phenomenon around the crack tip, heightening the propensity for brittle failure.

Hydrogen embrittlement of the nickel alloy UNS N07718 for two different heat-treating schedules

The role of the nickel alloy 718 microstructure has been widely discussed and it is well established the δ phase detrimental effect on the material’s ductility and toughness when exposed to hydrogen. However, other microstructural features that might influence the embrittlement process are more elusive, which requires more in-depth studies. Having selected heat-treating schedules to mitigate δ phase precipitation, this work aims to assess the hydrogen embrittlement of two alloy 718 variants with nominal yield strengths of 120 and 150 ksi. Fundamentally, the idea is to understand the extent of the hydrogen damage caused by an increase in mechanical strength beyond the limit of 140 ksi specified in the API 6ACRA. Slow strain rate (SSR) and fracture toughness (FT) testing were applied to evaluate the mechanical behavior under cathodic polarization. The microstructure of both variants is comprised of recrystallized austenite grains and a very low content of grain boundary δ phase. Nanosized disk-shaped γ″ particles are also present for both variants, although the 150 ksi material shows a higher volume fraction and a finer distribution of this phase. Despite having the same overall fracture features, nanostructure differences between the variants and the consequent impact on hydrogen apparent solubility and slip planarity produced lower values of plastic elongation and initiation fracture toughness for the stronger material.

Effects of printing patterns and loading directions on fracture behavior of 3D printed Strain-Hardening Cementitious Composites

Strain-Hardening Cementitious Composites (SHCC) have gained widespread attention as self-reinforcing materials in 3D concrete printing. Meanwhile, owing to the layer-by-layer build-up process during extrusion-based 3D printing, interfaces have a significant impact on the fracture behavior of 3D printed concrete. In this study, 3D printed SHCC (3DP-SHCC) specimens were prepared with two printing patterns: parallel-printing and cross-printing. Cubic compressive strength tests and three-point bending tests on notched beams were conducted. The results showed that the compressive strength of 3DP-SHCC was 1.23 ∼ 1.45 times higher than that of mold-cast SHCC. Parallel-printed SHCC exhibited a significant degree of anisotropy. The initial and unstable fracture toughness (KICini, KICun), flexural strength (Ff), and fracture energy (Gf) of parallel-printed SHCC in the X direction were 1.31, 1.81, 1.39, and 1.79 times those of mold-cast SHCC, respectively. In comparison, the cross-printed SHCC showed significantly lower anisotropy in the X and Y directions. By incorporating cohesive elements with the cohesive damage plasticity model, the fracture behavior of the 3DP-SHCC could be accurately simulated.

Effects of rolling process and microstructure on the brittle crack initiation and arrest of a marine steel under low‐temperature

AbstractThe effects of the rolling process and microstructure on the brittle crack initiation and arrest of marine steel were systematically investigated. The microstructures of two steel plates produced by different rolling processes were observed and analyzed. The results demonstrated that the rolling process significantly influenced the microstructure. As the rolling temperature decreased, the grain size decreased, the high‐angle grain boundary (HAGB) content increased, and the average grain misorientation angle increased. The brittle crack initiation and the arrest abilities were evaluated by initiation fracture toughness and crack arrest toughness, respectively. The initiation fracture toughness and crack arrest toughness increased with the decreasing grain size and the increasing content of HAGBs. Finally, the influence of microstructure on the brittle crack initiation and arrest ability was explained from two aspects: (1) the critical event of crack initiation at low temperatures, and (2) the hindering effect of HAGB on the propagation of brittle cracks.

Investigating the influence of various three-point bending specimen configurations on rock fracture parameters testing: an experimental study

The fracture parameters of rocks, including fracture toughness and fracture energy, represent their resistance to crack propagation under external stress. These parameters play a critical role in engineering design, construction safety, geological mechanics research, and rock material assessment. This study determined the fracture parameters of granite under Mode I loading conditions using notched semicircular bend (NSCB) and single-edge notched beam (SENB) specimens. Although there was little difference between the initial and unstable fracture toughness values of the two specimen configurations, significant differences were observed in the fracture process and other fracture parameters. For example, the NSCB specimen exhibits a higher elastic modulus, and it witnessed rapid failure after reaching the peak load, whereas the SENB specimen displayed a more gradual failure process with a distinct post-peak stage. This may be one of the reasons for the higher fracture energy in the NSCB specimen than in the SENB specimen. Based on finite element analysis and the extraction of the tangential stress at the crack tip region, the application of the maximum tangential stress fracture criterion provided a robust explanation for the coherence observed in the unstable fracture toughness test results between the two specimen configurations.

On the Cover: Effect of Loading Rate on Mode-I Crack Initiation Fracture Toughness of a NdFeB Rare Earth Permanent Magnet by B. Song, B. Sanborn, T. Martinez, D. Landry, C. Loeffler, R. Ferrizz, J. L. Pacheco

On the Cover: Effect of Loading Rate on Mode-I Crack Initiation Fracture Toughness of a NdFeB Rare Earth Permanent Magnet by B. Song, B. Sanborn, T. Martinez, D. Landry, C. Loeffler, R. Ferrizz, J. L. Pacheco

Study on fracture characteristics of steel fiber reinforced manufactured sand concrete using DIC technique

Incorporation of steel fibers to improve the defects of manufactured sand concrete (MSC) has received a great deal of attention, while the fracture mechanism of the MSC by volume fraction of steel fibers (Vf) has been less studied. To investigate the effects of steel fibers on the fracture characteristics of the MSC, three-point bending tests were conducted on the MSC beams with different Vf (0, 0.5 %, 1.0 % and 1.5 %) using digital image correlation technique. The effects of Vf on the fracture parameters and crack propagation paths of steel fiber reinforced manufactured sand concrete (SFRMSC) were analyzed. In addition, fracture process zone (FPZ) of the SFRMSC was analyzed via the length of the FPZ (lFPZ) and area of the FPZ (AFPZ). The results indicated that the residual strength, initiation fracture toughness, unstable fracture toughness, fracture energy and characteristic length of the SFRMSC increased with the increase of Vf, whereas the crack propagation paths were not sensitive to the changes of Vf. The addition of steel fibers increased the interaction between the aggregate and the matrix, which led to an increase in the number of microcracks. Before approaching the Pc, both the lFPZ and AFPZ showed essentially stable changes. As Vf increased, the lFPZ and AFPZ developed faster to their corresponding maximum values. The AFPZ reached a maximum and increased with the Vf. At the Pc, the lFPZ and AFPZ changed in a similar trend when Vf ≤ 1.0 %. When Vf > 1.0 %, the lFPZ changed slightly while the AFPZ increases sharply.

J-Integral Experimental Reduction Reveals Fracture Toughness Improvements in Thin-Ply Carbon Fiber Laminates with Aligned Carbon Nanotube Interlaminar Reinforcement.

The Mode I, Mode II, and mixed-mode interlaminar failure behavior of a thin-ply (54 gsm) carbon fiber-epoxy laminated composite reinforced by 20 μm tall z-direction-aligned carbon nanotubes (CNTs), comprising ∼50 billion CNT fibers per cm2, is analyzed following J-integral-based data reduction methods. The inclusion of aligned CNTs in the ply interfaces provides enhanced crack resistance, resulting in sustained crack deflection from the reinforced interlaminar region to the intralaminar region of the adjacent plies, i.e., the CNTs drive the crack from the interlaminar region into the plies. The CNTs do not appreciably increase the interlaminar thickness or laminate weight and preserve the intralaminar microfiber morphology. Improvements of 34 and 62% on the Mode I and Mode II initiation fracture toughness, respectively, are observed. This type of interlaminar nanoreinforcement effectively drives crack propagation from the interface to within the ply where the crack propagates parallel to the interlaminar region, providing new insight into previously reported strength and fatigue performance increases. These findings extend to industries where lightweight and durable materials are critical for improving the structural efficiency.

Theoretical and experimental study on mixed-mode I + II fracture characteristics of thermally treated granite under liquid nitrogen cooling

Liquid nitrogen fracturing technology is widely used in the exploitation of hot dry rock (HDR) geothermal resources. It is necessary to understand the fracture characteristics of hot dry rocks under liquid nitrogen cooling. In this study, the mixed-mode I + II fracture characteristics of the thermally treated granite under liquid nitrogen cooling were investigated. The results indicate that as the exposed temperature increases, the number of internal microcracks increases, while the fracture energy and fracture toughness of the granites decrease. From 25 ℃ to 600 ℃, mode I fracture toughness decreases from 1.286MP·m1/2 to 0.612MP·m1/2; mode Ⅱ fracture toughness decreases from 0.830MP·m1/2 to 0.413MP·m1/2; mixed-mode Ⅰ+Ⅱ fracture toughness decreases from 1.082 MP·m1/2 to 0.530MP·m1/2 at Me = 0.705 and from 0.914 MP·m1/2 to 0.445 MP·m1/2 at Me = 0.427, respectively. Additionally, the intergranular fracture behavior increases as temperature increases, resulting in an increase in irregularity of fracture surfaces. The generalized maximum tangential stress (GMTS) criterion is used for predicting the fracture characteristics (fracture initiation angle and fracture toughness) of thermal damaged granites. The accuracy of the GMTS criterion in predicting crack resistance when mode II loading dominates has been improved by considering the variation of critical damage radius.

Prediction of crack initiation for notched concrete beam from FPZ at maximum load

The initial cracking load (Pi) of a notched concrete beam, difficult to measure, has been predicted from the maximum fracture load (Pmax) together with the notch-tip fracture process zone (FPZ) at Pmax. A simple analytical model is used to link Pi and Pmax together through the FPZ. The corresponding initiation and unstable fracture toughness, Ki and Kun, have also been determined. The model assumes that the lower limit of Pmax from a group of identical notched concrete beams corresponds to the lower limit of the FPZ length FPZL, so that the lowest limit Pmax = Pi is established for FPZL = 0. Detailed FPZ measurements before and at Pmax using a digital image correlation technique were analysed and used to predict the initial cracking load Pi. Six different specimens with various sizes (W = 40, 60 and 80 mm), initial notches (a0 = 12 to 48 mm) and FPZL (7 to 13 mm) at Pmax showed the average ratio of FPZL/(W – a0) was around 0.25, indicating the Pi/Pmax ratio was around 0.67 based on the analytical model. The crack growth resistance KR-curve between the crack initiation toughness Ki at Pi and the unstable fracture toughness Kun at Pmax was also established approximately by the simple model. Estimated intrinsic fracture toughness KIC was compared with Ki and Kun. The influence of average aggregate size dav on Pi and FPZL at Pmax was also discussed.

Antibacterial and dynamical behaviour of silicon nanoparticles influenced sustainable waste flax fibre-reinforced epoxy composite for biomedical application

Abstract This article explores the impact of nano-silica on the properties of woven flax fibre/epoxy composites. Using compression moulding, epoxy/flax/silica hybrid nanocomposites were produced. The nano-silica was dispersed in the epoxy matrix via ultrasonication at various weight ratios. A series of tests, including crack durability, dynamic mechanical analysis, and scanning electron microscopy, were conducted to evaluate the modified materials. Notably, a 3% nano-silica filler load resulted in a 54% and 57% improvement in initiation and transmission interfacial fracture toughness, respectively. Scanning electron microscope imaging confirmed that fibres pull out at the crack tip during initial debonding, accounting for the increased toughness. Dynamic mechanical analysis further revealed enhancements in mechanical properties. Moreover, the 3% nano-silica content led to less fibre pull-out, suggesting higher heat resistance than standard flax/epoxy composites. The material also demonstrated promising antimicrobial efficacy against gram-positive and gram-negative bacteria, offering a potential alternative to conventional antibiotics.

Mechanical performance, impact behavior and environmental assessment of coal furnace slag based low-carbon ultra-high performance engineered cementitious composites (UHP-ECC)

This study aimed to optimize the utilization of industrial solid waste through developing a high-performance cement-based composite material (UHP-ECC), incorporating coal furnace slag (CFS) and waste rubber powder (RP). The investigation concentrated on the effects of introducing 10% RP into UHP-ECC and replacing ordinary Portland cement (OPC) with CFS at varying proportions (0%, 20%, 40%, 60%) on mechanical properties, impact resistance, and sustainability. The mixtures underwent a comprehensive characterization, including mechanical tests, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), to clarify hydration mechanisms and microstructural features. The results revealed that the addition of 10% rubber led to flaws, resulting in a minor reduction in compressive strength from 143.2 MPa to 132.2 MPa. Substituting 20% with CFS resulted in a denser matrix, raising the compressive strength to 135.5 MPa. CFS decreased the initial cracking strength and matrix fracture toughness, with tensile strain peaking at 8.05% and narrower crack widths. More CFS content yielded a slight decrease in peak impact force but induced more fine cracks and enhancing ductility. Moreover, as CFS is a waste product generated at high temperatures, the mixture demonstrated outstanding impact performance at 150 °C, absorbing rather than converting more energy into kinetic energy. Comparative analysis against similar mixtures highlighted UHP-ECC's strengths in embodied carbon, embodied energy, and material cost. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) assessment identified the CFS40-R10 as better mixture, achieving a balance between mechanical performance, cost-effectiveness, and sustainability. Microscopic analysis revealed that up to 40% CFS facilitated hydration, and the 60% CFS mixture exhibited the lowest total mass loss at high temperatures.

Combined Effects of Steel and Glass Fibres on the Fracture Performance of Recycled Rubber Concrete

As an environmentally friendly construction material, recycled rubber concrete (RRC) is commonly used as a road material owing to its excellent flexural strength and crack resistance. Previous studies have shown that the addition of fibres is an effective method for improving the crack resistance of concrete. The purpose of this study is to investigate the fracture performance of RRC reinforced with steel fibres (SFs) and glass fibres (GFs). A total of 28 RRC mixtures were prepared. The results of the fracture test showed that the addition of SFs and GFs significantly enhanced the RRC fracture performance. The maximum increases or decreases in flexural strength, brittleness coefficient, fracture energy, initial fracture toughness, and unstable fracture toughness were 64.9, −34.6, 775.6, 92.0, and 118.4%, respectively. The ideal GF content is usually in the range of 0.4–0.6% and decreases with increasing SF content. In addition, scanning electron microscope (SEM) tests were conducted to explore the mechanism of the effect of hybrid fibres on RRC at a microscopic level. The results show that SFs were always pulled out, while GFs were pulled apart at the initial defects. At the same time, excessive GFs caused more initial defects. These results are expected to provide theoretical direction and experimental support for the practical application of hybrid fibre-reinforced recycled rubber concrete (HFRRRC).

Impact of polyethylene fiber and microsilica on fracture properties of high strength high toughness geopolymer concrete (HSHTGC)

This study investigates the utilization of polyethylene fiber (PEF) and microsilica for the production of high-strength and high-toughness geopolymer concrete (HSHTGC). The influence of the PEF factor or microsilica content on fracture parameters and strength is evaluated, while acoustic emission (AE) response and crack morphologies are employed to validate the fracture performance results. By combing PEF with microsilica, this study successfully prepared HSHTGC with compressive strength exceeding 90 MPa, significant multi-cracking characteristics, as well as high toughness and ductility. The optimal microsilica content and fiber volume fraction are determined to be 32 wt% and 1.5 vol%, respectively. It is observed that when the fiber factor exceeds 800, there is a decline in compressive strength, initiation, and unstable fracture toughness, however, the fracture energy and ductility index consistently increase monotonically. These findings indicate that fiber toughening has a more pronounced effect than fiber strengthening. Moreover, microsilica plays a crucial role in filling voids and improving bonding between fibers and matrix under both tensile and compressive loads throughout the entire process. HSHTGCs with high fiber factors and increased microsilica contents exhibit a multi-cracking mode along with elevated RA values but reduced AF values during failure process, which correspondingly reflect their enhanced toughness.

Study on the fracture mechanical properties of high performance concrete (HPC) with rapid cooling after high temperature

In practical engineering, concrete structures typically undergo high temperatures and fire spray cooling during the process of fire, and high temperatures will cause changes in the microstructure of concrete. Therefore, studying the fracture mechanical properties of concrete after rapid cooling at high temperatures is more in line with the actual engineering situation. This paper sets five temperature conditions (20°C, 200°C, 400°C, 600°C, and 800°C), and after rapid cooling in a water bath, a hydraulic servo machine is used to conduct three-point bending beam fracture tests on plain concrete (PC) and high performance concrete (HPC). The fracture process and mechanism are analyzed using digital image correlation (DIC) and acoustic emission (AE). The research results indicate that the three-point bending unstable fracture load of PC and HPC decreases with the increase of temperature, with the maximum reduction after 800 ℃ high temperature, reaching 87.5% and 82.2%, respectively. After high temperature, the fracture energy of PC and HPC both showed a trend of first increasing and then decreasing. The ductility index of PC and HPC increases with the increase of temperature. The unstable fracture toughness and initial fracture toughness of PC and HPC decrease with the increase of temperature. By combining DIC and AE technologies, the development and fracture mode of cracks in PC and HPC after rapid cooling at high temperature are analyzed. The results showed that the softening effect of concrete is more significant after high temperature, the crack initiation stage is earlier, and the bearing capacity is lower. Furthermore, modern testing techniques are employed to reveal the mechanism of the impact of high temperature and cooling methods on the mechanical properties of HPC from a microscopic perspective. The research results have important reference value for practical engineering.

Research on the Fracture Behavior of Ultra-fine Dredged Sand Concrete Based on the Microstructure Characteristics

Abstract The dredged sand generated by the dredging projects has been abandoned and reclaimed from designated areas. It meets the requirements of environmental construction and resource utilization, if the dredging sand can be used as building material in construction. In order to investigate the fracture behavior of dredged sand concrete, five kinds of concrete with different dredged sand replacements (0 %, 12.5 %, 25 %, 37.5 %, 50 %) were designed in this article. Three-point bending fracture tests were carried out on the concrete. The test results show that with the increase of dredged sand replacement, the initiation load, peak load, fracture toughness, and fracture energy first decrease and then increase. Computerized tomography scan and mercury intrusion porosimetry tests show that with the increase of dredged sand replacements, the porosity, pore volume, and pore surface area increase first and then decrease. Dredged sand can improve the pore structure, increase the compactness of concrete, and improve the fracture behavior of concrete. Scanning electron microscopy and X-ray diffraction tests show that dredged sand mainly plays the role of physical filling, and proper dredged sand can improve the compactness of concrete.

Study on fracture characteristics and fracture mechanism of fully recycled aggregate concrete using AE and DIC techniques

Fracture behaviors of manufactured sand-recycled coarse aggregate concrete (MSRCAC), recycled fine aggregate concrete (RFAC), and fully recycled aggregate concrete (FRAC) were investigated by performing three-point bending tests on single-edge notched beams using acoustic emission (AE) and digital image correlation (DIC) techniques. The effects of recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and their interaction on fracture parameters, AE characteristics and fracture process zone (FPZ) of concrete were comparatively analyzed. The results indicated that it was mainly transgranular failure and intergranular failure for RFAC, while transgranular failure for MSRCAC and FRAC. The RFA and RCA reduced the initial fracture toughness, unstable fracture toughness and fracture energy of concrete, and their interaction resulted in poor fracture properties of FRAC. In addition, the RFA and RCA significantly increased the AE activities, the proportion of tensile cracks, and the high-frequency amplitude and peak frequency of concrete. The toughening effect of FPZ was weakened by the RFA and RCA, resulting in an obvious increase in FPZ length and damage propagation of FRAC. Meanwhile, the width of FPZ was reduced, the maximum FPZ width of concrete with different combinations of recycled aggregates was approximately 1.8–3.1 times the maximum aggregate size, which could be explained as the RFA and RCA reduced the aggregate interlocking effect of concrete, while the RCA had a greater effect on the damage mechanism and FPZ of concrete than the RFA.

Interleaving Carbon-Glass Veil in Glass Epoxy Composite for Improved Mode-I Fracture Toughness – A Hybrid Approach

The present study investigates the influence of hybrid interleaving technique using Glass and Carbon veils to improve the mode-I fracture toughness in Glass epoxy laminates. Commercially available non-woven Carbon and Glass veils with different areal densities were used to develop hybrid interleaved composites. Two approaches of interleaving, namely inter-ply and inter-weaved veils, were followed to manufacture the interleaved composite laminates using the hand layup technique. Double Cantilever Beam (DCB) samples were tested to estimate the interlaminar fracture toughness (IFT). Test results indicate that the inter-ply interleaved composite (I-C30G30) exhibited an improved initial and propagation fracture toughness of about 16.98% and 3.08%, respectively. A decreased IFT during initiation and propagation was observed for I-C15G30 and I-C20G30 when compared to plain samples. In case of inter-weaved veil interleaving approach, an improved fracture toughness (GIC and GIP) of about 7.96% and 12.94%, respectively, was observed for W-C15G30 sample, nevertheless W-C20G30 and W-C30G30 showed a drop in fracture toughness (GIC) of an about 12.15% and 9.22%, respectively, and an improvement in fracture toughness (GIP) of about 12.37% and 13.82%, respectively, when compared to plain sample. Scanning electron photo images (SEPI) of cracked laminates witnessed the fracture mechanisms involved in hybrid ply interleaved and non-interleaved composite laminates.