Evaluation Of Toughness Research Articles

Comparative study of toughness and energy evaluation of laminated bamboo composites and toughening mechanism

Comparative study of toughness and energy evaluation of laminated bamboo composites and toughening mechanism

Design and control the selection of martensitic variant to simultaneously improve strength and toughness of low-carbon martensitic steel

In this paper, the microstructure evolution and mechanical properties of low carbon steels during direct quenched and rolling followed by water-cooled processes were studied. Two experimental steels, which were directly quenched at 900 °C (Q900) and 1000 °C (Q1000), were compared with steels that were water-cooled after rolling at the same temperatures (R900 and R1000). Microstructural analyses using EBSD and TEM revealed that rolling reduced the size of prior austenite grains (PAGs), resulting in an average width of 3.6 μm, which influenced grain boundary distributions and variant selection. The best combination of strength, ductility and toughness was obtained in R900 steel, including tensile (with the yield strength of 1304 MPa, the total elongation of 22.95 %), Charpy impact (with the impact energy at 20 °C is 182 J), and fracture toughness evaluations (with the J1c is 326.28 KJ/m2), this demonstrates that R900 steel exhibited significantly enhanced strength and ductility compared to Q900 steel. Moreover, EBSD analysis of crack propagation paths highlighted the role of high-angle grain boundaries (HAGBs) in enhancing fracture toughness by deflecting cracks. These findings underscore the critical role of PAGs size in tailoring microstructures to achieve superior mechanical properties in low carbon martensitic steels, offering insights for advanced material design and application in demanding structural and industrial contexts.Keyworks.low-carbon martensitic steel; strength and toughness; martensitic transformation; ductile-to-brittle transition phenomenon; selection of martensitic variants.

The Acoustic Emission Testing in the Evaluation of Fracture Toughness of Brittle Materials.

Evaluating the fracture resistance of dental ceramics is essential for assessing their behavior. This study aimed to validate a custom load-to-fracture test for assessing fracture strength compared to a conventional method. Acoustic emission testing, a non-destructive (ND) lab test, was employed to evaluate the fracture toughness (FT) of brittle materials by capturing sound waves generated by crack formation in failing samples. A total of 130 samples, divided into three types (glass sheets, zirconia sheets, and monolithic zirconia crowns), were tested. The fracture loads were measured using both custom and conventional methods. The mean fracture loads for glass sheets were 650.46 N ± 110.38 (custom) compared to 691.41 N ± 155.92 (conventional). For zirconia sheets, the values were 95.25 N ± 7.78 (custom) vs 112.75 N ± 31.26 (conventional). Monolithic zirconia crowns showed mean fracture loads of 1108.99 N ± 327.89 (custom) compared to 1292.52 N ± 271.42 (conventional). Statistically significant differences were evident in all three types, indicating lower values with custom testing for all samples. The custom testing demonstrated an advantage in identifying cracks at lower loads, thereby enhancing the accuracy of fracture load values. Despite its limitations, the study suggests that the custom setup could be a viable alternative to conventional fracture load testing of brittle materials. However, further testing with more materials is recommended to enhance the results' accuracy and generalizability. The findings indicate that the custom load-to-fracture test can provide more accurate measurements of FT in dental ceramics, which is crucial for predicting their clinical performance and longevity. How to cite this article: Haddad C, Eng JG, Zoghbi AE. The Acoustic Emission Testing in the Evaluation of Fracture Toughness of Brittle Materials. J Contemp Dent Pract 2024;25(7):617-623.

Evaluation of mode-I delamination toughness of composites for automotive applications

Abstract With the increasing need for energy efficiency, fiber-reinforced composites are being widely used in the automotive industry. This study investigates the inter-laminar fracture behavior of fiber-reinforced composite double cantilever beam specimens considering a non-zero slope at the root. Experiments were conducted on unidirectional and cross-ply glass fiber reinforced epoxy composite specimens and the critical delamination toughness G I C has been evaluated by the proposed weighted residual equation. The proposed mathematical model requires crack length and the load versus displacement data to evaluate delamination fracture energy. This method accounts the measurement scatter and the rotation at the crack tip. For a particular specimen, the proposed model gives a unique value of critical delamination toughness value. The critical interface failure load estimates utilizing the evaluated delamination toughness agrees well with literature and in-house test results of double cantilever beam specimens.

Numerical calibration for fracture parameters of three-point bending semi-circular specimens

This study aims to refine the fracture characterization of three-point bending semi-circular specimens used in rock fracture toughness assessments. The primary objective is to improve the accuracy of such evaluations by developing numerical simulations of specimens with pre-engineered cracks of varying geometries. Numerical simulations were conducted using the finite element method. The interaction integral method was employed to quantify the stress intensity factors (SIFs) and T-stress at crack tips. Initially, the model’s accuracy was validated by replicating stress singularities at crack tips in a benchmark circular disk with a central straight crack. Following validation, dimensionless fracture parameters specific to the three-point bending semi-circular specimens were calibrated. The numerical results demonstrate that the dimensionless stress intensity factor (YI) increases with both the relative crack length (a/R) and the spacing between support points. Notably, for relative crack lengths a/R ≤ 0.5, the dimensionless T-stress assumes negative values, initially decreasing and then increasing as the relative crack length increases. The findings of this study provide valuable insights into the fracture behavior of three-point bending semi-circular specimens with pre-engineered cracks. Based on the observed trends in the dimensionless fracture parameters, it is recommended that relative crack lengths within the range of 0.2–0.6 be used to maintain the accuracy of rock fracture toughness tests. The finite element method used in this study serves as a robust tool for calibrating fracture parameters, thereby laying a strong foundation for the application of these specimens in rock fracture toughness evaluations.

Evaluation of impact toughness of glass-reinforced composite materials immersed in water

The mechanical and physical properties of glass fiber composite materials can be modified when immersed in water. This change in properties can result from internal instability of the material, interaction with the environment, mechanical stresses, or a combination of these effects. In this study fiber glass reinforced polyester resin plates have been manufactured by the contact molding method with 20% of reinforcement percentage. Prismatic specimens have been cut then notched to evaluate the impact toughness by applying the Charpy impact test. The Williams method based on the principle of linear elastic fracture mechanics was used to deduce the impact toughness of composite. These specimens have been immersed in water for 30 and 90 days to study absorption effect and diffusion on the impact behavior of this material. From the results, it is found that there is a direct correlation between water penetration in the glass-polyester composite and its impact toughness.

A Study on the Fracture Toughness Evaluation Considering Material Tensile Characteristic for Cryogenic Steel

Abstract ISO 12135, a representative standard for the evaluation of fracture toughness, was revised in 2021. In the previous standard published in 2016, only yield strength was reflected for material property in fracture toughness calculation. In the revised standard, however, yield to tensile strength ratio is additionally reflected in consideration of strain hardening effect of the material. The current fracture toughness calculation formula evaluates fracture toughness reasonably considering the tensile characteristic. However, in some cases of cryogenic steels, fracture toughness is evaluated very conservatively than the previous procedure in 2016. In the case of STS 304L, there is no ductile-brittle transition phenomenon and it has excellent ductility and strength in cryogenic temperature. However, due to the secondary hardening phenomenon, yield to tensile strength ratio is relatively low, and as a result, fracture toughness is evaluated very low. The target of this study is to resolve the undervaluation of fracture toughness of cryogenic steel in the revised ISO 12135. For this purpose, the elastic and the plastic parameters in crack tip opening displacement (CTOD) equation in ISO 12135 are examined. The crack tip profile is derived by a series of finite element analysis and crack tip opening displacement is calculated for the derivation of new parametric equations for cryogenic materials. The calculated crack tip opening displacement is validated by experimental results.

Full-scale test on the mechanical behavior of longitudinal joints of NC-UHPC composite segments under compression-bending load

The performance of longitudinal joints in shield tunnel segments is crucial for ensuring structural stability and durability. This study presents an innovative segment structure combining normal concrete (NC) and ultra-high performance concrete (UHPC) (hereafter called NC-UHPC composite segment). Full-scale joint tests were conducted to analyze the mechanical response and failure characteristics of longitudinal joints in these segments. Compared to reinforced concrete (RC) segment joints, NC-UHPC composite segment joints exhibited a significant increase in initial cracking load by 197.93% under sagging moments and 435.3% under hogging moments. The ultimate load-bearing capacity increased by 55.71% and 67.10%, and the initial bending stiffness improved by 20.57% and 10.59% under sagging and hogging moments, respectively. Furthermore, NC-UHPC composite segment joints exhibited smaller crack distribution areas and fewer cracks, indicating superior crack resistance. No cracks or damage were observed at the NC-UHPC interface. Evaluation of joint toughness and ductility indices further highlighted the favorable performance of NC-UHPC composite segment joints. Finally, a refined numerical model was established to compare the deflection and bending stiffness of RC segment joints with NC-UHPC composite segment joints under varying axial forces. The findings suggest that NC-UHPC composite segments are more suitable for tunnel engineering with greater burial depth, higher water pressure, and larger axial forces.

Experimental Study on Fracture Toughness of Shale Based on Three-Point Bending Semi-Circular Disk Samples

A large number of construction practice projects have found that there are many joints and microcracks in rock, concrete, and other structures, which cause the complexity of rock mechanical properties and are the main cause of geological or engineering disasters such as earthquakes, landslides, and rock bursts. To establish a rock fracture toughness evaluation method and understand the distribution range of fracture toughness of Longmaxi Formation shale, this study prepared three-point bending semi-circular disk shale samples of Longmaxi Formation with different crack inclination angles. The dimensionless fracture parameters of the samples, including the dimensionless stress intensity factors of type I, type II, and T-stress, were calibrated using the finite element method. Then, the peak load of the samples was tested using quasi-static loading, and the load–displacement curve characteristics of Longmaxi Formation shale and the variation in fracture toughness with crack inclination angle were analyzed. The study concluded that the specimens exhibited significant brittle failure characteristics and that the stress intensity factor is not the sole parameter controlling crack propagation in rock materials. With an increase in crack inclination angle, the prefabricated crack propagation gradually transitions from being dominated by type I fracture to type II fracture, and the T-stress changes from negative to positive, gradually increasing its influence on the fracture. An excessively large relative crack length increases the error in fracture toughness test results. Therefore, this paper suggests that the relative crack length a/R should be between 0.2 and 0.6. The fracture load distribution range of shale samples with different crack angles is 3.27 kN to 10.92 kN. As the crack inclination angle increases, the maximum load that the semi-circular disk shale samples can bear gradually increases. The pure type I fracture toughness of Longmaxi Formation shale is 1.13–1.38 MPa·m1/2, the pure type II fracture toughness is 0.55–0.62 MPa·m1/2, and the T-stress variation range of shale samples with different inclination angles is −0.49–9.48 MPa.

Mechanical mechanism of specimen size effect on impact toughness of Al 6061: Experiment and simulation

Impact toughness has a strong size effect, which restricts the accurate evaluation of material toughness and safety of structural design. However, our understanding of the internal mechanical mechanism that influences the size effect remains incomplete. To fill this gap, this paper adopts the method of combining experiment, theory, and simulation. From the point of view of the dependence of plastic and fracture behavior of material on stress state, the internal mechanical mechanism of the size effect of impact toughness (αk) was studied. Firstly, the Charpy impact tests of different sizes were carried out on Al 6061. αk was divided into cracking initiation toughness (αini) and cracking growth toughness (αgro). The variation of αini and αgro with specimen size was analyzed. Then, through a series of tests, the influence of stress state on the plastic and fracture behavior of Al 6061 was studied. To simulate the whole process of the Charpy impact test, an uncoupled 3D fracture model was proposed. Subsequently, a stress state dependent yield function, modified Voce hardening law, and the proposed fracture model were used to simulate the Charpy impact tests. The predicted results were in good agreement with the tests. Finally, the internal mechanical mechanisms of the size effects of αini and αgro were analyzed. The results show that: (1) The αini and αgro have significant size effects, and there are significant differences between them. (2) The internal mechanical mechanism of the size effect of αini was revealed; that is, the dependence of the plastic behavior of the material on the stress state is the internal root cause of the dependence of αini on the specimen size. (3) The internal mechanical mechanism of the size effect of αgro was revealed; that is, the dependence of the plastic behavior of the material on the stress state and the fracture behavior of the material under ultra-high stress triaxiality is the internal fundamental reason affecting the size effect of αgro. (4) This study reveals the internal complex and intimate relationships between plastic behavior, fracture behavior, toughness behavior, stress state, and the size effect, providing a valuable reference for accurate and comprehensive understanding, evaluation, and selection of metal materials.

Unveiling the Potential of Friction Stir Welding for Seamless Metal Joining

Friction Stir Welding (FSW) has revolutionized metal joining in manufacturing by offering robust joints without defects. This study examines FSW using specific parameters and evaluates its impact on mechanical properties and microstructure. Through rotational speed (2192 RPM), welding speed (36.3 mm/minute), tool tilt (3.4°), and concave shoulder angle (9°), FSW was applied to predetermined metal materials. Impact and Vickers tests were conducted post-welding to assess toughness, surface hardness, and microstructural changes. Results highlight the significant influence of FSW parameters on material properties, providing insights for optimizing efficiency and quality in the manufacturing industry. The study's findings contribute to addressing knowledge gaps and advancing FSW applications in industrial settings. Highlight: Precise Parameters: Control for strong joints in manufacturing. Toughness Evaluation: Assessing joint resilience under dynamic loads. Industry Optimization: Enhancing efficiency and quality in metal joining processes. Keywoard: FSW, Manufacturing, Mechanical Properties, Optimization, Impact Testing

The importance of fracture toughness evaluation for additively manufactured metals

Yield strength and fracture toughness are key properties of structural materials used by designers for engineering applications, whereas secondary properties like ductility are not generally used in quantitative design calculations. However, since ductility is usually measured along with strength in the same tensile test, it is often used as an indication of the fracture toughness even though these properties are usually not directly proportional. As a result, many researchers initially, and only, screen new materials and processing routes for good combinations of strength and ductility rather than evaluating fracture toughness independently. This can result in poorly informed decisions being made early in the development stages for structural applications where materials with combinations of high strength and good fracture toughness are required. In this article, we evaluate the correlation between fracture toughness and ductility of Al-, Fe-, and Ti-based alloys that were processed using conventional methods as well as by additive manufacturing (AM) routes. We highlight that the correlation between fracture toughness and ductility is very weak, which in the case of AM materials is attributed to their often-metastable microstructures, their layer-by-layer mesostructures, and their anisotropic failure characteristics that lead to pronounced variability in the fracture toughness data for materials with similar ductility. Our findings suggest that an independent assessment of fracture toughness alongside the tensile properties (strength and ductility) is required to correctly optimize the AM processing of structural materials and provide engineers with the properties required for the design of parts and components for structural and safety-critical applications.

Evaluating the Development Levels of Green Urban Transportation Systems

To promote the green and resilient development of urban transportation and the sustainable development of cities, we developed a technique that can be used to evaluate the level of urban green transportation development. First, the toughness evaluation indexes were integrated according to the connotation requirements of green transportation development, and the evaluation index system was constructed using the hierarchical analysis method. Second, subjective and objective weighting methods, such as the G1, entropy weighting, and “addition” integration methods, which provide a simple and easy-to-use evaluation method that can improve evaluation accuracy, were adopted. Finally, Harbin, a typical city in the north, was chosen as a representative city to verify the method effectiveness. The study findings can be used to evaluate the current level of green development of a city as well as for future planning, providing a basis for formulating sustainable urban transportation development strategies. We will continue to conduct comparative studies on different evaluation methods and cities to improve the generalizability of the method.

Comparative analysis of unloading compliance and normalization methods for fracture toughness assessment in 316L stainless steel at cryogenic temperatures

In the present study, the impact of test temperature, specimen geometry, and evaluation methodologies on the fracture toughness of 316L stainless steel was evaluated. Tensile and fracture mechanics tests were conducted utilizing a cryostat across a range of temperatures from ambient conditions to liquid hydrogen environments. The analysis of crack length prediction and resistance curve was performed using two fracture toughness evaluation methods: the unloading compliance method and the normalization method. The difference in fracture toughness by specimen thickness using the normalization method was within acceptable tolerances for all temperatures. However, fracture toughness evaluation using the unloading compliance method showed apparent negative crack growth at all temperatures, causing differences in J-integrals between specimen thicknesses and discrepancies between physical and estimated crack extensions. The application of the offset technique to the unloading compliance method significantly reduced these differences and made the J-integral of the normalization method and the unloading compliance method agree well. The substantial underestimation in the correction of the rotation angle at ambient temperatures was confirmed through real-time imaging of the crack tip with the unloading compliance method, which contributed to the large deviations between estimated and measured crack extensions.

Traction–separation law for bridged cracks at immiscible polymers interface

A traction–separation law for bonds at cracks bridged zones at immiscible polymers interface is developed. It is assumed that bonds at the crack bridged zone between different polymers are formed by bundles of the polymer molecules–promoter of adhesion. It is taken into account that molecules of the polymer-promoter can form one-stitch and many-stitch bonds between polymers. Nonlinear deformation curves of bonds at the crack bridged zone were obtained on this basis. The model of different materials joint with bridged interface crack is used to simulate immiscible polymers adhesive bonding. The system of singular integral-differential equations is applied for evaluation of bonds traction for the polymers interface bridged crack. The analysis of the bond traction–separation law parameters influence on the numerical iterative solution convergence of the integral-differential equations system has been performed. Evaluations of the polymer joint fracture toughness were performed using the non-local two-parameter criterion for quasi-static growth of bridged cracks.

Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study.

To evaluate and compare the fracture toughness and flexural strength of four different core build-up materials. A total of 60 samples were divided into four groups (n = 15) group I: dual cure composite resin reinforced with zirconia particles (Luxacore Z), group II: light cure composite resin (Lumiglass DeepCure), group III: zirconia reinforced glass ionomer cement (GIC) (Zirconomer Improved), and group IV: chemically cure composite resin (Self Comp) respectively. All the core build-up materials were manipulated according to the manufacturer's instructions and poured into the mold. A universal testing machine applied a central load to the specimen in a 3-point bending mode. Fracture of the specimen was identified and the reading was recorded by the universal testing machine. The data were analyzed statistically using one-way analysis of variance (ANOVA) and then compared. Group I showed the highest flexural strength (48.65 MPa) among all the groups while group IV showed the lowest flexural strength (17.90 MPa). Group I showed the highest fracture toughness (99.12 MPa) among all the groups while group IV showed the lowest fracture toughness (36.41 MPa.cm-0.5). When mean flexural strength and fracture toughness values of all four groups were compared by using one-way ANOVA, the compared data was highly significant. Based on the findings of this study, dual cure composite resin was the material of choice in terms of flexural strength and fracture toughness for core build-up material followed by light cure composite resin. The core buildup material serves to strengthen the tooth structure, allowing it to withstand the forces of chewing and preventing the risk of tooth fractures. This material is essential in restoring damaged or decayed teeth, as it provides a stable foundation for further dental work. By reinforcing the tooth structure, the core buildup material ensures that the tooth can function properly and remain healthy for years to come. How to cite this article: Nakade P, Thaore S, Bangar B, et al. Comparative Evaluation of Fracture Toughness and Flexural Strength of Four Different Core Build-up Materials: An In Vitro Study. J Contemp Dent Pract 2024;25(2):191-195.

Evaluation of microstructure and toughness of SAW steel weld metals with optimum Al/O ratio

Evaluation of microstructure and toughness of SAW steel weld metals with optimum Al/O ratio

Research on Flexural Properties and Flexural Toughness Evaluation Method of Steel Fiber Reinforced Cementitious Composites under Polar Low Temperatures

In this research, five groups of steel fiber reinforced cementitious composite (SFRCC) with different fiber volume content (0%, 0.5%, 1.0% 1.5%, and 2.0%) were designed to perform four-point flexural tests on beam specimens to study the effects of polar temperature (20, 0, −25, −50, −75, and −100°C) and fiber volume content on the flexural properties. The flexural toughness index and load holding capacity index were calculated based on the load–displacement curve, and the enhancement and toughening mechanisms of SFRCC by low temperature and steel fibers were analyzed in conjunction with experimental observations. The results of the proposed flexural toughness evaluation method show that the flexural toughness of SFRCC can significantly improve than that of ambient temperature when the temperature is lower than 0°C. With the decrease in temperature, the flexural property of SFRCC increases first and then decreases, and the temperature point of this transition is around −50–−75°C. The flexural property enhancement effect of 1.0% fiber volume content SFRCC is more significant in low temperatures according to the flexural toughness index and load holding capacity index. The conclusion can provide a reference for the application of SFRCC in cryogenic engineering, as well as a simple and quantifier evaluation method for flexural toughness is proposed.

Modelling of crack propagation in miniaturized and normal SENB specimens based on local failure criterion

The use of miniaturized specimen testing methods is a promising way to solve the problem of limited materials in RPV monitoring programs. The use of miniature specimens allows the evaluation of fracture toughness from other specimen materials used. In particular, the small-size compact tensile test specimen (0.16T CT) is promising for the determination of fracture toughness, as it can be produced from the standard size Charpy specimen that has already been tested. However, if we have only 0.16T CT test, we cannot investigate the dimensional response and also have only one restricted deformation state, which may pose problems in verifying geometry independence and determining local parameters for state-of-the-art analyses. It is therefore recommended to prepare at least two tests with two different restricted deformation specimens. Therefore, the testing of mini single edge notched bending (SENB) is also required and can be worked out from the Charpy specimens. The paper presents the determination of fracture toughness for these miniaturized specimens by modifying the virtual crack closure technique (VCCT) simulation method using GTN parameters instead of energy release as the driving force. This allows the calculation of the J-integral to proceed in parallel with the crack propagation.

Evaluation of fracture toughness according to the pre-strain and temperature effect with H-Section S420 steel for deep sea offshore structures

This study examined the effect of pre-strain on fracture toughness for H-section S420 steel base plates and welds, focusing on the significance of heat-affected zone (HAZ) fracture toughness after pre-strain. Once an offshore structure is installed, it is fixed in the same place for decades, making it essential to secure fracture stability against the damage that might occur owing to sea conditions. In particular, the effect of pre-strain on the fracture toughness of three types of specimens (without pre-strain, 3% pre-strain, and 6% pre-strain) was investigated. Further, an appropriate pre-strain amount in the offshore structure to ensure fracture safety was proposed. The damage suffered by the steel structure decreased for not only the base metal but also the weld joint. The H-section steel satisfied the requirement of critical crack tip opening displacement (CTOD) of up to 6% pre-strain in coarse grain HAZ (CGHAZ). Furthermore, the temperature satisfying the critical CTOD could be predicted using WES 2805.