Notch Length Research Articles

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.

Using removable sensors in structural health monitoring: A Bayesian methodology for attachment-to-attachment uncertainty quantification

Structural responses are vulnerable to perturbations when subjected to variable environmental and operational conditions, thereby contributing to the slow uptake of Structural Health Monitoring (SHM) beyond academic research. More importantly, SHM systems using removable sensors face additional sensing variability due to the inherent uncertainty in sensor reattachment compared to permanently attached sensors. In this study, a novel probabilistic approach is developed for output-only damage detection utilizing ultrasonic guided waves. Experimental uncertainties and sensor attachment factors are simultaneously considered for the first time in a Bayesian context. The uncertainty introduced by reattached sensors is incorporated into the likelihood function in a comprehensive way. Bayesian model class selection using an adaptive sampling scheme is adopted to evaluate the evidence of discrete damage classes. A reference case to an aluminum plate with progressive notches is utilized to demonstrate the significant effects of attachment uncertainty on guided wave signals. The optimal data normalization model for guided wave processing under different attachment states is evaluated using the Mahalanobis distance. The notch length is identified accurately along with the uncertainty, even though the latent adhesive parameters cannot be estimated directly.

Performance degradation evaluation of square steel tubes with local penetration damage

Steel tubular structures are susceptible to welding defects, cracking defects and environmental corrosion, which can negatively affect the stability and reliability of structure. This study tested the axial compression performance of twenty-six square steel tubular stubs with localized penetration damage simulated by artificial notch, considering the influence of notch length, orientation, and position. The test results showed that the failure mode of the specimens was dominated by the local buckling along the direction of the notch axis. The failure mode of the specimen with vertical notch showed notch opening, while those with horizontal notch showed notch closing, resulting in the secondary peak value in the load-displacement curve. The existence of local penetration damage reduced the ultimate strength and ductility of the tubular stubs. Compared to the ultimate strength of the specimens with middle notch, those with corner notch were weakened more, up to 27 %. Furthermore, the effects of notch dimension, position, orientation, and tube wall thickness on the axial bearing capacity of square steel tubular stubs are discussed by using a validated finite element model. Owing to the analysis, the ultimate strength of the stubs is reduced by increasing notch length, width and depth, whereas the reduction effect tends to be weakened as the notch orientation angle increases. The notch located in the corner is the most unfavorable for the axial compression performance of the square steel tubular stubs. A semi-empirical formula for evaluating the ultimate strength of square steel tubular stubs with local penetration damage is proposed by introducing the strength reduction factor. An artificial neural network-based ultimate strength prediction model is developed that can consider the effects of wide-range parameters, achieving high accuracy.

Rate dependent C* fracture parameter using the optimized wedge-split test geometry and vision-based automated crack tip detection

Typical monotonic load-line displacement (LLD) control and crack mouth opening displacement (CMOD) control cracking tests are limited to singular loading rates and testing temperatures. These experimental protocols are not designed to derive a fundamental fracture parameter capable of relating to the viscoelastic property and cracking behavior of asphalt concrete (AC). On the other hand, a multi-rate LLD-control monotonic fracture experiment is capable of capturing the viscoelastic cracking behavior of AC by providing the rate-dependent fundamental C* fracture parameter as an output. Crack length and crack speed parameters are combined with reaction loads to calculate the rate-dependent C* parameter. The current C* experiment protocol implements manual processing of video images and exhibits high variability. The study aims to optimize the wedge-split geometry and improve the C* fracture parameter calculation protocol by applying an automated vision-based crack detection system and recording the crack growth path, considering the horizontal and vertical movement of the crack tip with higher accuracy. The three notch lengths (5, 15, and 30 mm) were evaluated. Plant and laboratory-produced mixes with varying stiffness and fracture characteristics were included in the testing program. An optimized notch length for the test geometry was determined based on the on-specimen strain field observed using the digital image correlation (DIC) technique and crack path analysis. The optimum notch length was found to be 15 mm due to consistent strain localization at the crack tip and less crack deviation in the horizontal direction. The main contribution of this paper is the proposed vision-based crack path detection method, which enables measuring the crack path's true crack length and maximum horizontal deviation. The developed protocol and optimization of the testing geometry led to a significant improvement of the existing C* testing protocol, resulting in higher data quality and consistent results. The proposed protocol was validated using three comparable and distinctively different lab-produced mixtures. The results show that the C* experiment effectively differentiated between the mixes based on crack speed and the C* parameter.

Compression behavior and design optimization of triggered glass fiber reinforced polymer square tubes

AbstractGlass fiber reinforced polymer (GFRP) composite tubes have become increasingly popular in crashworthiness applications. On the other hand, square section GFRP tubes are prone to damage in a catastrophic failure mode in the early stages of the crushing process. At this point, triggering mechanisms have great potential to ensure deformation in progressive mode and improve the compression performance of GFRP tubes. Motivated by these facts, this paper aims to optimize the compression performance of square GFRP tubes by implementing notch‐type triggering mechanisms. The effects of notch width, number and length on the axial compression response of tubes were investigated to determine the optimal trigger configurations that would maximize specific energy absorption (SEA) and minimize peak crushing force (PCF). Experiments were conducted based on Taguchi L9 orthogonal array design, and Taguchi coupled Weighted Aggregated Sum Product Assessment (WASPAS) method was employed for optimizing multiple responses. The optimization results revealed that the proposed trigger mechanisms induced progressive crushing by preventing catastrophic failure, thereby significantly improving the compression performance of GFRP tubes. In particular, the results showed that the PCF of intact GFRP tube decreased by up to 38%, while SEA increased by up to 130% with the help of proposed trigger mechanism.Highlights The compression performance of square GFRP tubes improved by notch‐type triggering. The notch width, length and number were chosen as design parameters. Taguchi experimental design was used to find the best configuration of design parameters. The optimum configurations were examined through the entropy‐WASPAS approach. The results revealed that significant improvements can be achieved using trigger mechanism.

Variations of Tentorial Notch Anatomy in Autopsy and NCCT of Head Injury Patients to Correlate Its Impact over Brainstem—An Observational Study

Abstract Background Tentorium cerebelli divide cranial cavity into supratentorial and infratentorial compartment. Tentorial notch is a gap in tentorium cerebelli located centrally and anteriorly, related to upper brainstem, first six cranial nerves, cerebrum, and cerebellum. The aim of this study was to analyze morphometric variation in tentorial notch anatomy in autopsy and computed tomography (CT) of head injury patients and to find out correlation between tentorial notch anatomy and uncal herniation and changes over brainstem surface in case of uncal herniation. Materials and Methods Autopsy examination of head injury patients was done between July 1, 2021, and Jan 31, 2023. Skull was opened in a standard manner and midbrain sectioned at the level of tentorial edge. Tentorial notch parameters (anterior notch width, maximum notch width, notch length, posterior tentorial length, apicotectal distance, interpedunculoclival distance) were measured using geometry compass and vernier caliper. These parameters were also measured on noncontrast computed tomography (NCCT) head of same patients. Evidence of uncal herniation was sought for in both NCCT head and autopsy examination. Impact of uncal herniation over brainstem in form of indentation over lateral surface of midbrain and macroscopic brainstem hemorrhage was noted. Results In 65 autopsy cases, there were 56 male and 9 female specimens; their mean age was 40.63 ± 16.78 years (range: 7–86 years). The most frequent type of tentorial notch observed in our study was typical type (32.30%). Relative frequency of uncal herniation was present predominantly (75%) in large type of tentorial notch and least (20%) in small type of tentorial notch. A significant correlation (p-value < 0.01) was found between uncal herniation and indentation over lateral surface of midbrain, while no significant correlation (p-value > 0.05) was found between uncal herniation and macroscopic brainstem hemorrhage in autopsy specimens. Conclusion The results of our study provide a baseline data about tentorial notch anatomy and it may facilitate neurosurgical decision making as well as help in deciding the best trajectory for lesions approaching in the vicinity of the tentorial notch

Automated crack extension measurement method for fracture and fatigue analysis using digital image correlation

A novel Automated Crack Extension Measurement (ACEM) method based on combining decorrelation in strain field and a threshold near maximum of full-field strain obtained from digital image correlation, is developed in this work. A manual method for measuring crack extension from images of the specimen surface and ImageJ, was utilized to validate the accuracy of the proposed method. Initially, ACEM method was validated for crack extension under mode-I fracture of single edge notch specimens with different initial notch sizes. A satisfactory agreement was obtained from this analysis along with limits on the different parameter values used in ACEM. The method was then applied to low-cycle fatigue specimens with different initial notch lengths. Comparison of crack extension between ACEM and manual method reveals satisfactory agreement reinforcing the fidelity of the developed method for fracture and fatigue analysis. Fracture resistance and fatigue crack growth rate curves were also obtained for the different specimens.

Numerical simulation of axially loaded circular concrete-filled steel tubular short columns with localized corrosion

Concrete-filled steel tubular (CFST) columns are widely utilized in structures owing to their cost-effectiveness, high strength, ductility, and proven fire resistance. Despite these advantages, concerns persist regarding the performance of CFST columns with locally corroded steel tubes, impeding their widespread adoption in offshore structures. This research employs three-dimensional finite element (FE) simulations for circular CFST stub columns subjected to axial compression, validated against experimental data. Verification includes full load-displacement histories, ultimate axial strengths, and failure modes. The validated FE models are then employed to assess and compare the structural behavior of CFST columns with various shapes of localized corrosion, analyzing overall load-deformation curves, interaction stress-deformation responses, and composite actions. To acquire critical data for understanding stub column behavior, 81 specimens underwent non-linear finite element analysis, with local corrosion represented by artificial notches in steel tubes. Test parameters, such as notch orientations, lengths, depths, widths, and concrete compressive strength, are varied. Results elucidate the impacts of these parameters on different aspects of stub column responses with corroded steel tubes. Furthermore, the accuracy of existing design models in predicting the ultimate axial strengths of CFST columns with corroded steel tubes is assessed. Finally, through parametric analysis of test results, a practical model is proposed and verified for computing the peak resistance of a CFST stub column with a locally corroded steel tube.

Investigating the failure mechanism of X-shaped non-persistent joints under uniaxial loading: Experimental and numerical analysis

In this paper, rock samples containing non-persistent cracks of ‘‘X’’- shape were prepared and experimentally studied under uniaxial compression. Then, the numerical simulations of these tests were established using dynamic finite element software (LS-DYNA). Various joint configurations are assumed and their lengths are considered to change from the center of “X” in different rock specimens. The cracks propagation patterns, the failure processes, and energy absorptions during the tests are studied. The gypsum samples’ dimensions were 10 × 10 × 5 cm and one “X” shaped non-persistent crack was provided inside each specimen. The tensile strength of gypsum samples was 1 MPa. The notch's lengths are similar in some three cases while the length of one wing of the crossest joint varied in two other cases. In two residual cases, the length of the two wings of the crossest joint was varied. The opening of the crack was 1 mm. Angel between the notch trajectories was 90°. The model was subjected to an applied axial load rate of 0.05 mm/min. Results show that the failure mechanism of specimens was affected by notch length. The larger notch has a dominant effect on the breakage mode and failure strength. Newborn tensile cracks originated at the notch tip and propagated parallel to the loading axis to merge with the model boundary. Both the crack initiation stress and breakage stress were decreased by increasing the notch length. The absorbed energy has a minimum value when two large notches with a length of 6 cm exist in the model while it has a maximum value when notch lengths are equal to 2 cm. The increase in notch length resulted in a decrease in the difference between strains associated with crack initiation stress and final stress, indicating progressive breakage. Whereas the difference between strains associated with crack initiation stress and final stress was increased by decreasing the notch length, therefore delay failure occurred after crack initiation in the model. The results obtained from both laboratory experiments and numerical simulations show good agreement in the failure progression.

Experimental investigations of dry-dry timber-concrete composite notched connections designed for disassembly

Timber-Concrete Composite (TCC) decks offer an efficient, and environmentally friendly alternative to conventional concrete slabs. Traditionally the concrete is cast directly onto the timber with a permanent connection arrangement that does not allow non-destructive disassembly at end-of-service-life. This will prevent the reuse of the materials and ultimately decrease the extent of the environmental benefit. This paper presents a deconstructable dry-dry notched connection made from fully prefabricated timber and concrete elements. The concept was investigated through 30 experimental pure-shear push-off tests, where various design parameters, such as prestressing degree, fastener placement, and notch length, were varied. The experimental results indicate that the new connection exhibits the same stiffness characteristics as a traditional wet-dry notched connection. Five different failure modes were observed in the series, and experimental measurements such as Digital Image Correlation and fastener force measurement provided insight into the connection behavior during failure. Two rigid-plastic upper bound solutions were established to estimate the load-carrying capacity for two of the observed concrete failures, and a satisfactory agreement with the test results was obtained. In conclusion, the experimental results indicated that dry-dry notched connections are feasible for achieving a more environmentally friendly TCC structure.

Effect of loading direction and anatomical location on the ultimate tensile stress, fracture toughness, and failure patterns of knee meniscus

BackgroundRupture of the knee menisci is a common injury that can have implications for other conditions, such as osteoarthritis. The fracture toughness of soft tissue (Jc) is a mechanical property that characterizes its resistance to tear extension. To date, Jc of the meniscus has not been quantified. MethodsCyclic tensile tests were conducted on meniscus samples to determine Jc and explore its characteristics. Initially, the study investigated the impact of an initial notch on the ultimate tensile stress. This allowed for an understanding of how the presence of a notch affects its structural integrity. Subsequently, Jc was measured in both the radial and circumferential directions to assess its loading direction dependency. Furthermore, the study assessed the effect of anatomical location by comparing samples collected from the femoral and tibial layers. ResultsDefect tolerance of the meniscus is influenced by the loading direction. In the circumferential direction, the presence of an initial notch did not affect the ultimate stress, and no crack expansion was observed. In radial samples with a notch length of 40% or more of the total width, crack propagation occurred, leading to a decrease in the ultimate stress (p< 0.01). Additionally, Jc was found to be higher in the femoral layer compared to the tibial layer (p= 0.017). ConclusionThe study also examined the failure patterns of the meniscus to enhance our understanding of its pathology. These insights contribute to a better comprehension of meniscus injuries and can aid in the development of more effective treatment strategies.

Study on the Quasi-Ductile Fracture Behavior of Glubam: The Role of Fiber Distribution.

Cracking in fibrous composites is inevitable, and the fracture pattern is influenced by its fiber distribution. Bamboo fibrous composites have a distinct fiber distribution, which makes them an excellent material for studng the relationship between fiber distribution and fracture mode. Glued laminated bamboo is a bi-directional bamboo fibrous composite, which is called glubam for short. Its vertical thickness is about 28 mm, and the ratio of the number of longitudinal fiber layers to the number of transverse fiber layers is 4:1. This study conducted three-point bending fracture tests on single-edge notched specimens of glubam to investigate its mode-I fracture characteristics in the transverse vertical direction. The deformation curves show that the specimens still have the load-carrying capacity after reaching the maximum load, and the load shows a trend of step-like decrease, exhibiting a quasi-ductile fracture behavior. Overall, the fracture process can be divided into four stages, including linear, softening, quasi-ductile, and failure stages. In this study, based on certain assumptions, the prefabricated notch length a0 was adjusted according to the position of the transverse fibers. Subsequently, the non-linear elastic fracture mechanics method was employed to calculate the fracture parameters of glubam during the softening and quasi-ductile stages, including the fracture toughness KIC* and fiber tensile strength ft. The deviation of the fracture parameters between the two stages is within 10%, indicating that the correction of the a0 is correct. This indirectly proves that the staggered structure formed by longitudinal and transverse fibers is responsible for the quasi-toughness fracture of glubam. Finally, this study summarized and analyzed the quasi-ductile fracture behavior and found that materials or structures exhibiting quasi-ductile fracture behavior often possess a staggered structure. This staggered structure makes the crack in the form of semi-stable propagation, while the load decreases in a step-like manner.

A threshold criterion of stress intensity range in a steel sheet

Fatigue fractures often originate and propagate from geometric discontinuities or material defects in equipment or components. The occurrence and propagation of cracks near the fatigue limit were observed in notched specimens of a steel sheet that simulated this situation, and analyzed using fracture mechanics parameters. The notch caused strain concentration, and local plastic strain arose even at low stress amplitudes. Transgranular fracture occurred, and arrested cracks were observed near the threshold stress amplitude Δσth. The threshold stress intensity range ΔKth had a good power function correlation with the effective notch length aef, but it depended on the length and did not reach a constant value. By identifying and applying the critical power exponent, we proposed a prediction model using the function ΔKthc=Yπ1/2Δσthaef1/κ, which is the critical threshold stress intensity range that has a constant value. κ is equal to 5 for the steel sheet under transverse bending. Since ΔKth c obtained using this critical exponent method does not depend on the crack length, it can be used as a material constant and a failure criterion, and can be applied as a new strength prediction model.

Phase field approach to predict mixed-mode delamination and delamination migration in composites

In this work, we present a mixed-mode phase field approach to model delamination progression and its migration. The proposed model includes the volumetric and deviatoric effects that occur during the mixed-mode delamination and migration. The volumetric–deviatoric split is combined with a power law criterion of delamination to capture the mixed-mode effects. An anisotropic tensor is used in the crack surface density function for capturing the anisotropic fracture. Two history parameters are introduced to ensure the irreversibility of the damage field throughout the evolution process of delamination and to consider the maximum value of the strain energy. A staggered approach is implemented for solving the equilibrium and evolution equations. The algorithm enables to obtain stable numerical solutions with faster convergence. Several examples of mode I and mode II as per standard tests have been incorporated to demonstrate the working of the proposed method. The numerical examples are validated by comparison with experimental results from the literature. It is observed that the proposed model can predict crack paths and angles closer to the experimental results. Examples of multiple delamination and delamination migration are also studied to understand the kinking in the delamination scenario. It is observed that the delamination migration is governed by the ratio of notch length a to the distance of the load from the edge L, and by the stress state in front of the crack tip. In the case of laminates with multiple interphases, the event of delamination impinging and kinking at interphase depends on the fracture toughness ratio of the bulk and the interphase. The example of the single-edge notched composite lamina and open-hole tension test with different fiber orientations has been validated with the literature and experiments.

Research on the influence of parameters on the fracture performance of the large stone asphalt mixture based on the semi-circular bending test

Pavement failure is a main type of road damage. To investigate the fracture performance of asphalt mixtures with large aggregates, this study utilized the semi-circular bending test to compare the specimens of LSAM-30 (the large stone asphalt mixture) and AC-13 (the fine aggregate asphalt mixture). The research focuses on examining the effects of specimen thickness, notch length, loading rate, and test temperature on the fracture performance. In the assessment of the experimental outcomes, this study employs fracture energy, J-integral, BCI, and CRI as parameters for comparison. The findings demonstrate that under the same conditions, the large stone asphalt mixture exhibits higher peak load, greater fracture energy, higher BCI and CRI values, as well as better J-integral fracture toughness in comparison to the fine aggregate asphalt mixture. At 20°C, the crack path in the large stone asphalt mixture (LSAM) circumvented the large aggregates and thus presented to be bent and long, while the crack in the fine aggregate asphalt mixture was shorter and straighter. The longer and more curved crack path in the LSAM consumed greater energy, resulting in better fracture resistance. At 0°C, the cracks in both asphalt mixtures were linear, but the large aggregate mixture required a stronger load to damage the larger aggregates. Therefore, the LSAM demonstrates a slightly better fracture resistance at low temperatures. In conclusion, the higher peak load, fracture energy, BCI, and CRI of the LSAM indicate a superior fracture performance. The longer and more curved crack path implies greater energy consumption during the fracture. As a result, the LSAM exhibits better fracture performance and resistance to pavement failure compared with the fine aggregate asphalt mixture.

New method for determining the mode I fracture toughness of shotcrete: edge-notched partial disc test

The fracture toughness (mode I) of shotcrete specimens was obtained using edge-notched partial disc (ENPD) specimens. Notched Brazilian discs (NBDs) were also tested to validate the results of the ENPD experiments. Numerical analysis was also conducted on the ENPD results to compare the measured and numerically obtained fracture toughness values. The notch lengths in the ENPD specimens were 15, 30, 45 and 60 mm, while the notch lengths in the NBD specimens were 10, 20, 30, 40, 50 and 60 mm. It was found that the flat joint model accurately predicted the potential crack growth path and crack initiation stress as compared with the experimental results. It was also deduced that the fracture toughness was roughly the same with an increase in the notch length. The tensile strength (σt) and fracture toughness (KIC) of the shotcrete specimens were found to be meaningfully correlated (σt = 7.92KIC). The ENPD tests yielded the lowest fracture toughness values because of the pure tensile stress distribution on the failure surface. It was also found that the derived fracture extension patterns from the laboratory investigations were in acceptable agreement with the outputs of numerical simulations.

Gray correlation analysis between mechanical performance and pore characteristics of permeable concrete

Pervious concrete is a type of sustainable construction material used in pavement engineering due to its advantages in water permeability, skid resistance, and sound absorption performance. This study investigated the pore characteristics of five types of pervious concrete, along with the uniaxial compression behaviors and semi-circular bending (SCB) fracture performance. The critical stress intensity factor was obtained using the equivalent energy approach. Gray relational analysis was conducted between the mechanical performance and the pore characteristics. Pore indicators include the effective porosity, 2D porosity along the specimen height, 2D coordination number (CN) along the specimen height, 2D pore radius, 2D specific surface area, 3D CN, 3D pore radius, and 3D virtual porosity. Results indicated that from M1 to M3, when cement mortar content decreased from 520 kg/m3 to 408 kg/m3, the effective porosity increased from 18.95% to 27.43%, and the compressive strength and fracture toughness decreased obviously. For the same type of pervious concrete mixture, with the increase of notch length, the critical stress intensity factor decreased accordingly. The 2D porosity distribution, 2D pore size distribution, and 2D CN distribution presented a symmetrical trend of decreasing, then increasing, and then decreasing with the increase of specimen height. Aggregate with the gradation within the range of 9.5 mm to 19.0 mm generated a higher compressive strength, larger effective porosity and larger pore size compared to the gradation of 4.75 mm∼9.5 mm. The results of CN and pore radius generated from the 3D pore network model were larger than the corresponding 2D values. The gray correlation analysis revealed that 2D pore radius and 3D pore radius played critical effects on the uniaxial compressive strength and fracture resistance, while 2D CN and 3D CN were the least significant factors affecting the mechanical performance.

Plane Stress Fracture Toughness Testing of Freestanding Ultra-Thin Nanocrystalline Gold Films on Water Surface.

Fracture toughness, which is the resistance of a material to crack propagation, is a critical material property for ensuring the mechanical reliability of damage-tolerant design. Recently, damage-tolerant design is introduced to flexible electronics by adopting micro-cracked ultra-thin nanocrystalline (NC) gold films as stretchable electrodes in a plane stress state. However, experimental investigation of the plane stress fracture toughness of those films remains challenging due to the intrinsic fragility from their sub-100nm thicknesses. Here, a quantitative method for systematically evaluating the plane stress fracture toughness of freestanding ultra-thin NC gold film on water surface platform is presented. After effectively fabricating single-edge-notched-tension samples with femtosecond laser, mode I stress intensity factors are measured in the plane stress state on water surface. Moreover, investigation regarding the effect of notch length, notch sharpness, and notch tip plasticity validates this method based on linear elastic fracture mechanics theory. As a demonstration, the thickness-dependent plane stress fracture toughness of ultra-thin NC gold films is qualitatively unveiled. It is revealed that the thickness confinement effect on grain boundary sliding induces a transition in fracture behavior. This method is expected to further clarify the fracture-related properties of various ultra-thin films for next-generation electronics.

High-resolution induction thermography for detection of micro-cracks in Ti-6Al-4V alloys

ABSTRACT This study focuses on establishing a non-contact Non-Destructive Testing (NDT) method for detecting micro-cracks in Ti-6Al-4 V sample using the Eddy Current Thermography (ECT) technique. The study employs an induction coil for heating the sample and a thermal camera equipped with magnifying lenses to monitor surface temperature distribution. The variations in the thermal image signify the presence of defects. The efficacy of the proposed method is demonstrated through the examination of four samples featuring artificially created short notches, representing micro-cracks. These notches vary in dimensions, with notch openings approximately 20 µm, notch depths ranging from 1–10 µm, and notch lengths varying from 5 to 150 µm. The investigation explores the influence of the length and depth of short cracks on defect detection, revealing an increase in thermal contrast with both the length and width of the cracks. All notches are successfully detected using the proposed method, showcasing its applicability for real crack detection. The study concludes with the successful application of the method on a sample with actual cracks measuring less than 10 µm in width, 2 µm in depth, and a length of 100 µm.

Experimental investigation on I-II mixed mode fracture of hot mix asphalt using double-edge notched Brazilian disk test

The I-II mixed mode fracture is a typical failure pattern observed in asphalt pavement. In this study, the fracture behavior under I-II mixed mode of three diverse asphalt mixtures was scrutinized. The investigation involved performing double-edge notched Brazilian disk (DNBD) tests at two different temperatures: −10 °C and 25 °C. DNBD specimens were prepared with two notch lengths (10 mm and 20 mm) and seven notch angles, including 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Stress intensity factor (KIC and KIIC), equivalent stress intensity factor (K*IC and K*IIC), and fracture energy were used to characterize the fracture behaviors. The findings suggest that the generation of mixed-mode fractures can be manipulated through variations in notch length and angle. An increase in notch angle shifted the fracture behavior towards a more mode I-dominant pattern, while elongating the notch length amplified the significance of mode II fracture contributions to the overall fracture process. The influence of reclaimed asphalt pavement (RAP) on the fracture performance of asphalt mixtures exhibited variation across the temperatures ranging from −10 °C to 25 °C. At −10 °C, mixture C, which contained an SBS-modified binder, demonstrated the most robust fracture performance, as evidenced by higher values of KIC and KIIC. This was succeeded by mixture B that used a #70 binder, with mixture A incorporating RAP trailing behind. Conversely, at 25 °C, the presence of RAP contributed to achieving the highest indices of K*IC and K*IIC, surpassing even the performance of mixture C with its SBS-modified binder, followed by mixture B with its #70 binder. For specimens with identical notch lengths and angles, the stress intensity factors recorded at −10 °C were substantially higher compared to those at 25 °C. This observation suggests that fracture resistance diminishes as temperature rises. Furthermore, an increase in notch angle correlated with a reduction in fracture energy at −10 °C, whereas at 25 °C, the notch angle’s influence on fracture energy appeared to be negligible. When examining the performance at −10 °C, mixture C exhibited the highest fracture energy, with mixtures B and A following in descending order. In contrast, at 25 °C, mixture A outperformed mixtures C and B in terms of fracture resistance, as gauged by fracture energy. Notably, the effect of mixture type on fracture energy was consistent with the effect of mixture type on stress intensity factor.