Fracture Toughness Values Research Articles

Hybrid Geopolymer Composites Based on Fly Ash Reinforced with Glass and Flax Fibers

This article’s aim is to analyze physical, mechanical, and fracture properties as well as the thermal investigation of geopolymer composites reinforced with flax, glass fiber, and also the hybrid combination of fibers. Two types of matrices were considered as composites matrices. The first composition was based on fly ash and river sand. The second matrix composition contained fly ash and glass spheres. The content of reinforcement was 1% by mass. Compressive strength and three-point bending fracture tests were performed. The values of fracture toughness and fracture energy were determined. The resonance method was used to verify the dynamic characteristics, such as the dynamic modulus of elasticity and the dynamic Poisson ratio. The results show that single-type fibers in composites based on fly ash and glass spheres did not affect compressive strength. However, introducing hybrid reinforcement increased compressive strength by about 10% compared to the reference specimens. Flax fibers and hybrid reinforcement ensured higher fracture toughness and energy. The results also revealed great potential for glass sphere application to geopolymer materials in terms of fracture mechanics and thermal properties. Despite the lower strength properties in relation to geopolymers based on sand aggregate, applying reinforced fibers into the composite with glass spheres enhanced the compressive strength compared to other materials. Materials modified with glass spheres have a thermal conductivity twice as low as that of materials containing river sand.

Notch Effect in Acrylonitrile Styrene Acrylate (ASA) Single-Edge-Notch Bending Specimens Manufactured by Fused Filament Fabrication

This paper analyses the notch effect in the fracture behaviour of acrylonitrile–styrene–acrylate (ASA) material manufactured by fused filament fabrication (FFF). The research is performed on 72 single-edge-notch bending (SENB) specimens containing U-notches with nominal notch radii varying from 0 mm (crack-like defects) up to 2.0 mm, and fabricated with three different raster orientations (0/90, 45/−45, 30/−60). Apparent fracture toughness values are obtained for the different conditions and the resulting notch effect is analysed through the Theory of Critical Distances. A fractographic analysis is also performed using Scanning Electron Microscopy (SEM) in order to justify the fracture (macroscopic) behaviour from the observed fracture micromechanisms. The notch effect observed in the three ASA raster orientations is very similar, and lower than that observed in other FFF polymeric alternatives (ABS, PLA).

In situ synthesis, mechanical properties, and reaction mechanism of the WB2–SiC composites

AbstractIn the present work, WB2–SiC composite powders containing 20 vol.% of SiC were in situ synthesized by the boro/carbothermal reduction with WO3, SiO2, B4C, and carbon black as raw materials at 1400°C, 1500°C, and 1600°C, respectively. The as‐synthesized composite powders were then consolidated by spark plasma sintering (SPS) technique to obtain WB2–SiC composite bulk samples. The experimental results showed that the relative density of the WB2–SiC composite ceramic samples achieved in this study was higher than 97.5%. Also, electronic microscopy observations showed that SiO2 had reacted completely during the preparation process, and the SiC grains were homogenously embedded among the WB2 grains with the formation of a three‐dimensional structure. The Vickers hardness and fracture toughness values of the composite ceramic fabricated by powder heat treated at 1400°C were 24.6 ± 0.7 GPa and 5.4 ± 0.7 MPa·m1/2, respectively, which were the highest among three samples prepared in this study.

Fracture toughness in SPCC/CFRP hybrid laminates: Mode I and mode II perspectives

Hybrid composites using adhesive joints are gaining popularity in various industries as their various material combinations can create certain advantages. This research focuses on examining the mode I and mode II fracture toughness characteristics of the combined laminate between Steel Plate Cold Rolled Commercial (SPCC) metal and Carbon Fiber Reinforced Polymer (CFRP) composite processed using adhesive bonding. SPCC/CFRP hybrid laminate composites were manufactured with a variety of manufacturing options (A, B, and C) to find the most optimal method using two types of epoxy and cyanoacrylate adhesives, with two different bonding processes: secondary bonding and co-bonding. Fracture toughness values were measured through the Double Cantilever Beam (DCB) test for mode I and the End Notched Flexure (ENF) test for mode II. The test results showed that epoxy adhesives in the SPCC/CFRP adhesive joints provided better fracture toughness performance, especially when combined with the co-bonding technique. Specimens from manufacturing option C showed the highest GIC and GIIC values of 83.05 and 254.94 J/m2, respectively. These values increased by 58.98 % and 80.48 % compared to manufacturing options A and B in Mode I. Additionally, the GIIC value for manufacturing option C increased by 78.00 % and 66.76 % compared to manufacturing options A and B. The SPCC/CFRP hybrid laminates showed adhesive failure on the SPCC surface when using epoxy adhesive, whereas adhesive failure occurred on the CFRP surface with cyanoacrylate adhesive for the different manufacturing options.

Evaluation of Asphalt Anti-Cracking Performance of SBS Polymer with SCB Method and Deep Learning

In recent years, there have been unprecedented developments in artificial intelligence. Object detection, voice recognition, face recognition etc. are some of the artificial intelligence applications. In this study, an auxiliary method for the automatic detection of cracks, one of the main deterioration problems on highways, is proposed. The crack formation of hot mix asphalts is investigated with an image processing method modeled with Attention SegNet architecture. Styrene-butadiene-styrene (SBS), the most widely used additive in bitumen modification, was used at 2%, 3%, and 4% ratios to modify 50/70 bitumen. Semi-circular asphalt specimens obtained with SBS modified bitumen were subjected to a semicircular bending (SCB) test and fracture performance was investigated. The effects of different temperature, notch size and additive on crack detection performance are evaluated. In the experimental study, maximum load, fracture energy, fracture toughness (KIC) values were obtained at low temperature, and resistance values against crack propagation were obtained by applying the J-integral method at intermediate temperature. The results demonstrated that with the addition of SBS, the fracture strength and maximum load values increased at each temperature value, with the 4% SBS mixture offering the highest performance. Moreover, the image segmentation performed with SegNet provided high accuracy and precision values for cracks. It was observed that the accuracy values of the image processing methods decreased at low temperature, while at high temperature, higher accuracy values were obtained as the cracking rate.

Reactive molecular dynamics of the fracture behavior in geopolymer: Crack angle effect

Reactive molecular dynamics was applied in this study to construct the sodium aluminosilicate hydrate (N-A-S-H) and tensile fracture models with various crack angles. The impact of crack angle on the behavior of N-A-S-H fractures was explored while considering structural mechanical properties and energy evolution. Furthermore, the fracture toughness and brittleness index for various crack angle models were calculated. The findings indicated that the ultimate strength and elastic modulus of the fracture models grew linearly with the increase in crack angle. The fracture toughness value progressively grew while the model’s elastic energy efficiency and new surface energy efficiency decreased simultaneously. The 45° crack model possessed the largest oblique crack development surface in the fracture process due to the coupling effect of tensile and shear stress. Its elastic energy efficiency decreased as well the most, while the new surface energy efficiency increased and the fracture toughness value dropped sharply. It is crucial to place a stronger emphasis on spotting cracks both in the in-service structures or structures being demolished. This ensures optimal performance and safety by enabling more effective adjustments to the direction of external forces and energy input.

Fracture analysis of seawater sea-sand recycled aggregate concrete beams: Experimental study and analytical model

Seawater sea-sand recycled aggregate concrete (SSRAC) has garnered significant attention from engineers involved in various coastal engineering projects. Fracture constitutes one of the primary failure modes of SSRAC, and the accurate analysis of its fracture behavior is crucial for application. In this present study, SSRAC with 50% aggregate replacement was subjected to three-point bending tests to evaluate its fracture performance. Specific methodologies for calculating SSRAC fracture toughness were introduced, taking into account the effects of material microstructures and specimen boundaries. By comparing the fracture properties of SSRAC specimens with varying initial notch lengths, the size effect was addressed by using established methods, resulting in a constant fracture toughness value. Furthermore, the methods for analyzing the fracture of un-notched specimens were developed, considering fracture path analysis and the influence of internal defects. Notably, this research demonstrated that small specimens and established methodologies efficiently predict the fracture behavior of larger specimens, providing practical insights for engineering applications.

Interlaminar fracture properties of UV and plasma‐treated glass fiber epoxy composites

AbstractDespite the low density and high specific strength properties, the fiber‐reinforced composites are characterized by a relatively low interlaminar fracture toughness and their ultimate properties are strongly affected by the fiber matrix adhesion. This study aims to investigate the influence of fiber surface treatments, such as UV and atmospheric plasma, and of the interfacial shear strength, on the flexural properties and Mode I interlaminar fracture toughness of glass fiber epoxy composites. The vacuum‐assisted resin infusion technique is used for the composite fabrication. Scanning Electron Microscopy analysis is used to observe and to explain the changes in the morphology of the fibers after surface treatment. Remarkably, the results showed an overall reduction in the mechanical properties. The interfacial shear strength values of the UV and plasma‐treated samples were reduced by 34.9% and 49.5% respectively. The flexural strength was reduced by 7.9% and 5.9% respectively. The Mode I fracture toughness values for the UV and plasma‐treated samples were also reduced by 49.8% and 62.2% respectively.Highlights UV and plasma treatments were performed on glass fibers to improve performance. Push‐out tests were carried out to evaluate fiber/matrix adhesion. An aerospace grade epoxy resin curing in thermal press‐clave was used. Mechanical tests related Interfacial Shear Strength to composites performance.

A probabilistic model to predict specimen geometry effects on fracture toughness in ferritic–pearlitic steels

This work describes a probabilistic framework for cleavage fracture of ferritic–pearlitic steels incorporating experimental measurements of microcrack distribution associated with the cracking of the pearlitic microstructure. A central objective of this study is to explore and further extend application of a probabilistic framework incorporating the statistics of microcracks to predict specimen geometry effects on the fracture toughness distribution for a typical ferritic–pearlitic structural steel. Fracture toughness values for an ASTM A572 Grade 50 structural steel derived from fracture tests using conventional SE(B) specimens with varying thickness and a/W-ratios provide the cleavage fracture resistance data needed to assess specimen geometry effects on the probability distribution of Jc-values. The present exploratory study successfully predicts the measured statistical distribution of cleavage fracture toughness in shallow crack specimens and provides further support of the proposed probabilistic model as a more advanced and effective engineering-level procedure in fracture assessment methodologies.

FABRICATION OF AA1100/Fl2O3 COMPOSITE STRIPS AND THE IMPROVEMENT OF THEIR ELECTROMAGNETIC, MECHANICAL AND FRACTURE PROPERTIES

In this study, forming limit diagrams (FLDs), fracture toughness (FT), mechanical, magnetic, and electro-physical properties of Al/Fe2O3 composites have been investigated experimentally. Accumulative-roll-bonding (ARB) process was used to manufacture composite samples. Then, Al/Fe2O3 composites have been produced at 300∘C up to eight ARB passes. Also, magnetic composites have been fabricated with 0, 5% and 10[Formula: see text]wt.% of particles. The interlayer bonding quality was improved at higher passes. By studying the SEM rapture morphology, it was shown that the rapture mode changed to shear ductile for samples with more passes. For composite samples fabricated at higher passes and in comparison with the annealed sample, elongated dimples were turned to shallow dimples. FLDs area as the main forming criterion dropped severely after pass one and then began to improve at higher passes. Fracture test results showed that after the 8th pass, the value of FT improved gradually to the maximum value of 34.3[Formula: see text]MPam[Formula: see text].

Accurate comparison of the fracture toughness of ultra-thick polycrystalline diamond plates by ISO standard method

Due to the difficulty in preparing ultra thick diamonds, current research on the mechanical properties of diamonds mostly focuses on thin samples, which cannot represent the true mechanical properties. In this study, DC arc plasma jet chemical vapour deposition method was used to deposit ultra-thick diamond plate measuring Ø125 mm × 6.5 mm. The size of 18 mm × 4 mm × 3 mm sample were prepared. The samples with dimensions of 18 mm × 4 mm × 3 mm were prepared. For the first time, fracture toughness test samples meeting the ISO 15732 requirements were prepared by using the single-sided beam pre-crack method. The accurate fracture toughness of ultra-thick diamond with pre-crack was obtained using the three-point bending method, 6.5 MPa·m1/2. Samples with sharp or blunt notch by laser cutting were used for comparison. The sharp notch sample had a value similar to that of the pre-crack sample, 6.3 MPa·m1/2. The value of the blunt notch sample was relatively large, 7.5 MPa·m1/2. The effects of defects and grain size on fracture toughness and the reasons for the differences in test results for different notches were analyzed. Overall, obtaining accurate fracture toughness values of ultra-thick diamond by ISO standard is crucial for industrial applications.

Effect of artificial aging on fracture toughness and hardness of 3D-printed and milled 3Y-TZP zirconia.

This study aimed to evaluate the impact of artificial aging on the fracture toughness and hardness of three-dimensional (3D)-printed and computer-aided design and computer-aided manufacturing (CAD-CAM) milled 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). Forty bar-shaped specimens (45 × 4 × 3mm) were prepared using two manufacturing technologies: 3D printing (LithaCon 3Y 210, Lithoz GmbH, Vienna, Austria; n = 20) and milling (Initial Zirconia ST, GC, Japan; n = 20) of 3Y-TZP. The chevron-notch beam method was used to assess the fracture toughness according to ISO 24370. Specimens from each 3Y-TZP group were divided into two subgroups (n = 10) based on the artificial aging process (autoclaving): nonaged and aged. Nonaged specimens were stored at room temperature, while aged specimens underwent autoclave aging at 134°C under 2bar-pressure for 5 h. Subsequently, the specimens were immersed in absolute 99% ethanol using an ultrasonic cleaner for 5 min. Each specimen was preloaded by subjecting it to a 4-point loading test, with a force of up to 200 N applied for three cycles. Further 4-point loading was conducted at a rate of 0.5mm/min under controlled temperature and humidity conditions until fracture occurred. The maximum force (Fmax) was recorded and the chevron notch was examined at 30 × magnification under an optical microscope for measurements before the fracture toughness (KIc) was calculated. Microhardness testing was also performed to measure the Vickers hardness number (VHN). A scanning electron microscope (SEM) coupled with an energy dispersive X-ray unit (EDX) was used to examine surface topography and chemical composition. X-ray diffraction (XRD) was conducted to identify crystalline structure. Data were statistically analyzed using two-way ANOVA and Student's t-test with a significance level of 0.05. The nonaged 3D-printed 3Y-TZP group exhibited a significantly higher fracture toughness value (6.07MPam1/2) than the milled 3Y-TZP groups (p < 0.001). After autoclave aging, the 3D-printed 3Y-TZP group maintained significantly higher fracture toughness (p < 0.001) compared to the milled 3Y-TZP group. However, no significant differences in hardness values (p = 0.096) were observed between the aged and nonaged groups within each manufacturing process (3D-printed and milled) independently. The findings revealed that the new 3D-printed 3Y-TZP produced by the lithography-based ceramic manufacturing (LCM) technology exhibited superior fracture toughness after autoclave aging compared to the milled 3Y-TZP. While no significant differences in hardness were observed between the aged groups, the 3D-printed material demonstrated greater resistance to fracture, indicating enhanced mechanical stability.

Fracture toughness of mixed-mode anticracks in highly porous materials

When porous materials are subjected to compressive loads, localized failure chains, commonly termed anticracks, can occur and cause large-scale structural failure. Similar to tensile and shear cracks, the resistance to anticrack growth is governed by fracture toughness. Yet, nothing is known about the mixed-mode fracture toughness for highly porous materials subjected to shear and compression. We present fracture mechanical field experiments tailored for weak layers in a natural snowpack. Using a mechanical model for interpretation, we calculate the fracture toughness for anticrack growth for the full range of mode interactions, from pure shear to pure collapse. The measurements show that fracture toughness values are significantly larger in shear than in collapse, and suggest a power-law interaction between the anticrack propagation modes. Our results offer insights into the fracture characteristics of anticracks in highly porous materials and provide important benchmarks for computational modeling.

Reversible photochromic effect and excellent mechanical properties of Nd3+-doped Zr6Nb2O17 purple ceramics

The development of colored ceramics is limited because it can only display a single color. Therefore, colored ceramics that can achieve reversible switching between two different colors can make up for this deficiency. In this study, we report a novel rare-earth doped colored ceramic, Zr6Nb2O17: xNd3+ (abbreviated as ZNO: xNd), which has been successfully obtained with good mechanical and photochromic properties of purple ceramics by component adjustment. The doping of rare earth Nd3+ ions changed the color of the ceramic matrix from light curry to light purple, and more importantly, enhanced its mechanical properties, with optimal Vickers hardness and fracture toughness values of 16.53 GPa and 5.2 MPa·m1/2, respectively. Alternating 365 nm irradiation and 350°C thermal stimulation, the ceramic samples exhibited good photochromic properties, with the highest photochromic contrast of 21.1 %, and good reversibility and cyclic stability. Finally, it is important to clarify that the photochromic mechanism is mainly caused by the formation of color centers resulting from electrons or holes being trapped by intrinsic or extrinsic defects. These results indicate that ZNO: xNd purple ceramics can be applied in the field of colored ceramics and provide a new path for the development of rare earth-colored ceramics.

Liquid Hydrogen Properties Affecting Fracture Toughness

In this study, fracture toughness with the base metal of 9% Ni steel, a cryogenic steel, was evaluated under conditions without hydrogen charging (WO-H) and with hydrogen charging (W-H). Hydrogen charging was performed using an electrochemical cathodic charging method in a electrolyte of 3% NaCl + 0.3% NH4SCN at 19℃ with a current density of 50 A/m². Fracture toughness was assessed at -80℃, -100℃, -130℃, and -160℃ using CTOD (Crack Tip Opening Displacement) tests. The results for WO-H indicated a decrease in fracture toughness values with decreasing temperature, while the results for W-H showed an increase in fracture toughness values as the temperature decreased. In addition, the fracture surfaces and fracture toughness of WO-H and W-H became increasingly similar as the temperature decreased, as observed through scanning electron microscopy (SEM). At -80℃, there was a significant difference in fracture toughness between the WO-H and W-H conditions. WO-H was influenced only by the low temperature, whereas W-H was affected by both low temperature and hydrogen, showing combined effects that led to a decrease in fracture toughness due to hydrogen embrittlement. However, at -160℃, the fracture toughness values for both WO-H and W-H conditions were nearly identical. This suggests that the temperature effect on fracture toughness reduction is greater than hydrogen embrittlement at very low temperatures.

Zirconia specimens printed by vat photopolymerization: Mechanical properties, fatigue properties, and fractography analysis.

The mechanical and fatigue properties of zirconia specimens printed by vat photopolymerization (VPP) were evaluated and compared with those of zirconia specimens milled by computer numerical control (CNC). Bar-shaped specimens were printed by stereolithography (SL) and digital light processing (DLP). CNC-milled specimens were used as control samples. The fracture toughness, hardness, and flexural strength properties of the zirconia specimens were evaluated via single edge V-notch beam tests, Vickers hardness tests, and 3-point bending tests. Dynamic fatigue tests were carried out in distilled water using a step-stress test. After static bending and dynamic step-stress testing, fractography analysis was performed. Statistical analysis was carried out to compare the fracture toughness, hardness, flexural strength, and fatigue cycle results of each group (α = 0.05). The fracture toughness values did not significantly differ among the groups (p>0.05). The flexural strength was 894.10MPa for SL, 831.46MPa for DLP, and 1140.39MPa for CNC. The flexural strength of CNC was greater than that of SL and DLP (p<0.01). The mean fatigue cycles were 23498.07 for SL, 19858.60 for DLP, and 31566.80 for CNC. The mean fatigue failure strength was 643.13MPa for SL, 530.63MPa for DLP, and 903.75MPa for CNC. The fatigue failure strength of CNC was greater than that of SL and DLP (p<0.05). Fractography analysis revealed material defects at the fracture origin for each group. A partially fused structure of the incompletely debonded resin could be observed in SL, and a porous region of incompletely sintered zirconia grains could be observed in CNC. The fracture toughness and hardness of zirconia printed by VPP are comparable to those of zirconia milled by CNC. However, zirconia milled by CNC has superior static flexural strength and dynamic fatigue resistance. Further studies are needed to explore the clinical applications of VPP-printed zirconia.

Effect of gadolinia–stabilized zirconia nanoparticles manufactured from Mist CVD on the mechanical properties of ceramics sintered by SPS

Zirconia is an engineering ceramic material with excellent comprehensive properties. However, it suffers from the inherent disadvantage of low fracture toughness. To improve its fracture toughness, Gd2O3 is an effective stabilizer. In the present study, Gd2O3–ZrO2 composite powders were synthesized using the Mist CVD method. Following synthesis, these powders were pressed through spark plasma sintering. The crystallinity of the Gd2O3–ZrO2 powders improved as the deposition temperature increased from 600°C to 900°C. The tetragonality (c/2a) of the Gd–TZP composites increased from 0.99941 to 1.01571 as the Gd2O3 content increased from 2 mol% to 4 mol%, but it decreased when the content reached 5 mol%. The Gd2O3–ZrO2 nanoparticles produced via the Mist CVD approach presented a unique hollow spherical structure. Under moist chemical vapor deposition (CVD) conditions with 4 mol% Gd2O3 at 1400°C, the Gd–TZP composites exhibited fracture toughness and hardness values of approximately 12.03 ± 0.15 MPa·m1/2 and 12.16 ± 0.17 GPa, respectively.

Improving properties of boron carbide (B4C) with silicon doping and titanium diboride addition

In this research, B4C-TiB2 composites were successfully fabricated via the spark plasma sintering method. First, the TiB2 source effect on the B4C-TiB2 composites was investigated using commercially available TiB2 and in-house synthesized TiB2. Subsequently, the effect of Si/B co-doped B4C on composite ceramics was studied, followed by examining the samples' microstructure and elastic and mechanical properties. The results showed that B4C-TiB2 composites made with in-house TiB2 powder obtained higher relative density and more desirable elastic and mechanical properties than samples made with commercial TiB2. In-house TiB2 and Si/B-B4C composites provided more properties improvement overall. The elastic modulus, Vickers hardness, and fracture toughness values of Si/B co-doped samples were 493 GPa, 30.09 ± 1.97 GPa, and 4.31 ± 0.74 MPa m1/2, respectively. Additionally, the amorphization of the TiB2-B4C composite decreased with Si/B co-doping.

Influence of processing parameters on the fracture behaviour of 316L SS printed by laser powder bed fusion

This study explored the relationship between process parameters and fracture behavior in 316L stainless steel printed by laser powder bed fusion. Fracture testing was conducted according to ASTM E1820 for single edge notch bending, and elastic mechanical properties were determined using ultrasonic surface wave analysis. Five test sets were considered in a vertical building configuration using five different volumetric energies belonging to conduction mode. The critical fracture toughness was calculated and discussed along with the plastic deformations at the crack tip. The study found that local plastic deformation for single edge notch bending was influenced by powder bed fusion process parameters. A correlation was observed between energy density, fracture toughness, and the dimensions of the fracture process zone. The R-curves showed different fracture behaviors depending on the energy density. The energy required to grow a crack was associated with larger plastic zones, resulting in fracture toughness values ranging from 43 (43 J mm−3) to 427 kJ/m2 (68 J mm−3). Results are discussed in terms of porosity and strain hardening capacity depending on the manufacturing conditions.

Simulation Analysis of Three-Point Bending Fracture Process of Yellow River Ice

During the ice flood period of the Yellow River, the fracture and destruction of river ice can easily lead to the formation of ice jams and ice dams in the curved and narrow reaches. However, the occurrence and development mechanism of river ice fracture remain incompletely understood in the Yellow River. Therefore, based on the three-point bending physical test of the Yellow River ice, a three-point bending fracture numerical model of the Yellow River ice was constructed. The fracture failure process of the Yellow River ice under three-point bending was simulated, and the effects of the crack-to-height ratio and ice grain size on the fracture properties of the river ice were analyzed. By comparing the results with those of physical tests on river ice, it is evident that the fracture model can effectively simulate the cracking process of river ice. Within the confines of the simulated sample size spectrum, as the crack-to-height ratio varies from 0.2 to 0.8, the fracture toughness value of the Yellow River ice spans a range from 115.01 to 143.37 KPa·m1/2. Correspondingly, within the simulated calculation values ranging from 5.38 mm to 24.07 mm for ice crystal size, the fracture toughness value of the Yellow River ice exhibits a range from 116.89 to 143.37 KPa·m1/2. The findings reveal that an increase in the crack-to-depth ratio leads to a decrement in the fracture toughness of river ice. Within the scale range encompassed by the model calculations, as the average size of the ice crystal grains augments, the fracture toughness of the river ice exhibits a gradual ascending trend. The research results provide a parameter basis for studying the fracture performance of the Yellow River ice using a numerical simulation method and lays a foundation for investigating the cracking process of river ice from macro and micro multi-scales.