Fracture Failure Research Articles

Crack Propagation in Axial-Flow Fan Blades Under Complex Loading Conditions: A FRANC3D and ABAQUS Co-Simulation Approach

Since fan blades are exposed to fatigue, and in some cases harsh loading conditions, they may exhibit fracture failures due to crack propagation, resulting in significant losses. Previous studies of crack propagation in blades are mainly confined to either simplified blade geometry or loads, resulting in a significant discrepancy between the simulated crack propagation and the real blade propagation behavior, while it is lacking for challenging shapes and loads. A co-simulation approach of FRANC3D and ABAQUS was developed to study the crack propagation of an axial-flow fan blade subjected to centrifugal, aerodynamic, and combined loads. The projected approach is validated with results obtained from analytical calculations and experiments. Meanwhile, making use of benchmarks, the Stress Intensity Factor (SIF) and the prediction of mixed-mode crack growth path are validated. Considering various loads, the crack propagation path response for the fan blade is computed for different growth steps. The results pinpoint that the crack propagation length of the crack tip center is maximum under centrifugal loading. However, the aerodynamic load led to a maximum propagation length of the crack tip endpoints. In addition, the combined force of centrifugal and aerodynamic loads limits the crack from growing.

Fracture resistance, failure mode and restorability of CAD CAM Zirconia endocrowns with different pulpal extension depths bonded to maxillary molars: an in-vitro study

BackgroundPulpal extension depth (PED) is critical for endocrowns restored teeth stability and longevity. There is a conflicting result regarding the minimum PED needed for the success of endocrowns. The aim of the current study was to compare Fracture resistance, failure mode, and restorability of CAD-CAM zirconia endocrowns with different pulpal extension depths bonded to maxillary molars.Materials and methodsForty maxillary 1st molars were selected, decoronated, and randomly divided into 4 main groups (n = 10) according to the PED measured from the pulpal floor to the occlusal end of the wall height into; group D2, PED was 2 mm, group D3, PED was 3 mm, group D4, PED was 4 mm, group D5 PED was 5 mm. Teeth were prepared and secured in resin dies with pseudo periodontal ligament. Specimens from all groups were individually scanned using an intra oral digital scanner. Monolithic zirconia endocrowns were constructed and bonded to their corresponding. Following thermal cycling, each specimen was axially loaded in a universal testing machine at a 0.5 mm/min crosshead speed. Failure modes were inspected, and restorability of specimens was recorded. Data was collected, tabulated, and statistically analyzed.ResultsDescriptive statistics displayed higher mean value of the D2 group (3657 1673.8 N) followed by the D3 group (3009.3 853.5 N), then the D4 group (2087.3 413.9 N) and finally the D5 group (1972.7 ±330.4 N). At a 95% confidence level, one-way analysis of variance (ANOVA) revealed significant differences between tested groups. (P = 0.014). Regarding failure mode, D2 recorded 100% restorable failures, followed by D3 (90%) and D4 (60%), while the least was D5 (50%).ConclusionsEndocrowns with 2 mm PED recorded the highest fracture resistance and the highest restorable failure modes. Endocrowns with 5 mm PED recorded the lowest fracture resistance and the lowest restorable failure modes. Tall walls should be shortened during the preparation of endocrowns in maxillary molars.

A comparative evaluation of the resistance to vertical root fracture after removal of separated instruments using three instrument retrieval systems: An in vitro study

Abstract Introduction: Separated instruments have been retrieved from root canals using different systems of instruments. However, it has been a common observation that usage of available retrieval systems may weaken the roots of teeth making them prone to fracture and subsequent failure of the treatment as a whole. Hence, the following study was conducted to evaluate and compare the resistance to vertical root fracture after retrieval of separated instruments from the root canal using Ultrasonic U Files, Ultrasonic Tip (Acteon Endo Success ET25 Retreatment Tip), or the Endo Rescue System under magnification of the dental operating microscope. Materials and Methods: Forty-two moderately curved mesiobuccal roots of extracted decoronated mandibular first molar teeth were hemisectioned to standardize them to a length of 15 mm each. Following biomechanical preparation, 4-mm length ProTaper gold rotary finishing files F2 were intentionally separated in the middle third of the mesiobuccal root canal and verified radiographically. The samples were then randomly divided into three groups, and retrieval of the separated instrument was performed using the Ultrasonic U files, Ultrasonic ET25 Retreatment tip, or Endo Rescue System, respectively. After retrieval of the separated instruments, the samples were subjected to testing for vertical root fracture resistance using a universal testing machine with an accuracy of ± 1%. The data collected from all the samples were then subjected to statistical analysis. Result: Ultrasonic U files (Group A) showed the highest vertical root fracture resistance, with a statistically significant difference from the samples treated with ET 25 Ultrasonic retreatment tips(Group B). No significant differences were observed between Group A and C or Group B and Endo Rescue System (Group C) (P > 0.05). Summary and Conclusion: It was observed that Ultrasonic U files offer the least reduction in the vertical root fracture resistance after removal of separated instruments followed by the Endo Rescue system and then the ultrasonic ET25 retreatment tips. While no single instrument retrieval system is universally suitable for all situations due to various factors such as root anatomy, instrument type, location, size, pulpal status, and operator skill, clinicians should determine the treatment protocol by carefully considering the tooth’s future prognosis.

Spinopelvic Fixation Using an Osseointegrative Implant: Analysis of Postmarket Surveillance to Determine the Failure Rate.

Adult spinal deformities, affecting up to 60% of individuals older than 60 years, often require long segment fusions. Constructs spanning the lumbosacral junction commonly include pelvic fixation. Despite robust pelvic fixation, distal junctional failure, such as pseudoarthrosis, bone fracture, and instrumentation failure, occurs in 24%-34% of these cases. A novel implant designed for both durable pelvic fixation and sacroiliac joint fusion was recently cleared by the US Food and Drug Administration. This implant is engineered to address some of the pelvic fixation failure mechanisms by reducing motion at the lumbosacral junction and sacroiliac joint while decreasing stress on S1 pedicle screws and S2AI implants. To determine the failure rate of a novel osseointegrative implant for spinopelvic fixation/fusion. Analysis of manufacturer postmarket surveillance database. A postmarket surveillance database was analyzed to determine the type and rate of complaints and revisions of a novel osseointegrative implant. These were then compared with the published literature. A total of 15,628 implants were identified in 6907 patients. The postmarket surveillance of the novel screw fusion device revealed a low complaint rate of 0.75% and no postoperative implant breakage. Revision procedures were mostly due to set screw dissociation (0.4%) and implant loosening (0.15%), which was primarily linked to pre-existing conditions or infection. The mean (SD) time from index procedure to the complaint was 7.1 (5.4) months. Compared with published literature, this novel osseointegrative implant demonstrates a significantly lower incidence of set screw dissociation than traditional pelvic screws with no incidence of breakage or back out, underscoring its durable integration with bone, with low rates of revisions and mechanical failures. A novel osseointegrative implant offers reduced rates of mechanical failures and revisions, helping to reduce complications in pelvic fixation procedures.

An In-Vitro Investigation into the Fracture Resistance of Prefabricated and Custom-Made Zirconia Crowns for Permanent Molars in Children

Background: Recently, the demand for esthetic restorations has grown dramatically and extended into the pediatric population. The prefabricated zirconia crowns (PZCs) and custom-made zirconia crowns (CZCs) are new esthetic options in pediatric dentistry. However, they are still inadequately tested for use in children. Aim: To determine the fracture resistance and failure mode of the PZC in comparison to the CZC. Materials and methods: In this in-vitro study, thirty cobalt-chromium dies were fabricated by scanning the negative replica of a prefabricated lower first permanent molar zirconia crown. CZCs were designed and milled using two different zirconia brands: Ceramill Zolid-FX (FX) and the Highly-Translucent (HT) zirconia. Dies were randomly assigned to receive either a PZC or a CZC (n = 10 in each group). All crowns were cemented on their respective dies using glass ionomer cement. Following artificial aging, all specimens were loaded to failure. Fracture mode analysis was performed. One-way ANOVA and Bonferroni post-hoc test were used for multiple comparisons across the groups. The significant level was set at p ≤ 0.05. Results: HT zirconia had a significantly higher fracture load compared to other groups (p < 0.05). The mean fracture resistance values were: (3087 ± 385) N for HT zirconia, (2633 ± 300)N for PZCs, and (2483 ± 381)N for FX, with no statistically significant difference in fracture strengths between PZCs and FX. Conclusion: HT zirconia crowns showed the highest fracture resistance amongst all groups. The fracture loads of tested crowns exceeded the maximum posterior biteforce. When placed in permanent molars, PZC are expected to perform well under masticatory forces in children.

Mixed-mode fracture analysis of notched components - An empirical failure equation

Abstract The mixed-mode failure problem of notched components remains a complex subject. On the basis of the multiaxial fatigue limit equation by Liu and Yan, in this study, an empirical failure equation to assess mixed-mode fracture of notched components is proposed. By using the test data of mixed-mode fracture failure of notched components from the literature, including the rounded-tip V-notched Brazilian disc specimens, rectangular plate specimens with a central blunt U-notch with different notch radii and notch angles, the empirical failure equation has been verified to be not only simple in computation form but also high in accuracy.

Fracture Resistance of Anterior Teeth Restored with Post-retained Ceramic Crown vs Ceramic Endocrowns.

To compare the fracture resistance of anterior teeth restored with either glass fiber post (GFP) and conventional lithium disilicate (LDS) crowns or endocrowns made of LDS or hybrid ceramics. A total of 21 central incisors with 2-mm ferrule and 1-mm shoulder finish line were applied in this investigation. The teeth were divided into three main groups (n = 7) according to the type of restoration used: PC glass fiber post (GFP) and e-max crown, EE (LDS endocrown), and VE (Vita-Enamic endocrown). Mechanical cyclic loading was conducted in a chewing simulator to simulate 6 months of clinical use. Fracture resistance and failure mode were assessed; further examination of fractured specimens was done with scanning electron microscopy. Post-hoc Tukey's test was performed to investigate the pairwise differences in fracture resistance among the three groups, and the results were p = 0.0452 between PC and VE groups, which is significant statistically. In contrast, p = 0.0615 between PC and EE groups, which is not significantly different. Chi-square test was made to analyze the results of mode of failure among the three groups, and there was a significant difference; p-value = 0.0289. The LDS endocrowns show fracture resistance similar to that of GFP-supported full coverage LDS crowns, with advantage of more restorable mode of fractures. Vita-Enamic endocrowns, despite having fracture resistance lower than other groups, showed fracture resistance higher than the physiologic load, with restorable fractures more than both LDS endocrowns and GFP LDS crowns. For dental practitioners, endocrowns in damaged anterior endodontically treated teeth provide similar fracture resistance to GFP and full crowns, with the advantage of more restorable fractures if occurred. How to cite this article: Mohamed AA, Badawy MBA, El-Kouedi AMY, et al. Fracture Resistance of Anterior Teeth Restored with Post-retained Ceramic Crown vs Ceramic Endocrowns. J Contemp Dent Pract 2024;25(11):1045-1051.

Investigation of the Microstructures and Fracture Failure Mechanisms of Metal Active Gas Welded Joints of Dissimilar 304 Stainless Steels and Q235B/Q345 Low-Carbon Steels

Investigation of the Microstructures and Fracture Failure Mechanisms of Metal Active Gas Welded Joints of Dissimilar 304 Stainless Steels and Q235B/Q345 Low-Carbon Steels

Effect of polyethylene glycol on rheological, thermo‐mechanical, and tribological behavior of epoxy

AbstractOver the past few years, polyethylene glycol (PEG) has been recognized as an effective blend to enhance the mechanical properties of brittle epoxy. However, the literature contains limited systematic studies evaluating PEG's role in improving epoxy performance. Therefore, a systematic approach was employed in the present study to assess the impact of varying weight percentages of PEG on the viscosity, thermo‐mechanical, and tribological properties of epoxy. Adding 10 wt% PEG (PEG‐10) in epoxy is identified as the threshold limit. With PEG‐10, the viscosity significantly decreased by approximately 78%, while fracture toughness, tensile strength, tensile modulus, and failure strain improved by 59.5%, 38.5%, 37.8%, and 54%, respectively, compared to neat epoxy. Additionally, the wear rate was significantly reduced by 92% compared to neat epoxy, though thermo‐mechanical and flexural properties were slightly compromised. Furthermore, the failure mechanisms of the tensile fracture surfaces and wear tracks of epoxy–PEG blends were examined to understand PEG's role more comprehensively.Highlights A Significant drop in the viscosity of epoxy resin is achieved with the help of PEG‐400. PEG‐400 is mixed with epoxy resin to improve its fracture toughness and tensile properties. A 92% reduction is observed in the wear rate when PEG‐400 is mixed with epoxy resin at 10 wt%.

Mechanical Response of Mudstone Based on Acoustic Emission Fractal Features

In this study, the effect of the stress amplitude on the mechanical behavior of mudstone was systematically investigated by cyclic loading and unloading experiments and acoustic emission (AE) monitoring. The results show that at low-stress amplitudes, mudstone specimens show better elastic recovery ability, lower damage accumulation and higher structural stability. At high-stress amplitudes, the irreversible damage of the mudstone increases significantly, the internal fractures gradually expand and penetrate through, and the risk of instability increases significantly. This is manifested by the gradual increase in cumulative irreversible strain of mudstone at different stress amplitudes, up to 0.144%. In addition, different stress amplitudes have significant effects on energy evolution characteristics, with low-stress amplitudes mainly showing elastic deformation and a high percentage of recoverable energy, while high-stress amplitudes show a high percentage of dissipated energy. Under the condition of high-stress amplitude, such as the mudstone specimen #4, the percentage of tensile failure is 81.15%. Tensile failure dominates at all stress amplitudes, where the failure mechanism within mudstone is mainly characterized by the extension of tensile-type fractures. Through the multifractal analysis of AE signals, this study reveals the effect of the stress amplitude on the fracture extension mode and failure mechanism of mudstone. As the stress amplitude increases, Δα and Δf show an increasing trend. This indicates that the fracture extension process transforms from a relatively homogeneous and simple mode to a more inhomogeneous and complex mode. This transformation reflects the nonlinear and multiscale fracture characteristics of mudstone under high-stress conditions. The results of this study help to understand the mechanical behavior of mudstone under cyclic loading during coal mining and provide theoretical support for safe coal production.

Comparative Evaluation of Fracture Resistance and Failure Modes in Endodontically Treated Teeth Restored With Zirconia-Reinforced Lithium Silicate and Cast Metal Alloys: An In Vitro Study

Comparative Evaluation of Fracture Resistance and Failure Modes in Endodontically Treated Teeth Restored With Zirconia-Reinforced Lithium Silicate and Cast Metal Alloys: An In Vitro Study

Effect of Cervical Margin Relocation With Different Injectable Restorative Materials on Fracture Resistance of Molars Received MOD CAD/CAM Onlay Restorations.

To investigate the effect of cervical margin relocation with four different injectable restorative materials on the fracture resistance of molars receiving mesio-occluso-distal CAD/CAM nanoceramic onlay restorations. One hundred and five sound mandibular molars received a standardized mesio-occluso-distal onlay preparation, with cervical margins located 2 mm apical to the cemento-enamel junction. The molars were randomly allocated into five groups (n = 21) according to the cervical relocating materials used: Group I had no cervical margin relocation; Group II used a highly viscous glass ionomer; Group III used a highly-filled injectable resin composite; Group IV used a resin-modified glass ionomer; and Group V used a bioactive ionic resin. All groups received immediate dentin sealing before nanoceramic resin-based CAD/CAM onlay restorations. After the specimens were subjected to thermo-mechanical loading, they underwent fracture resistance testing and failure mode analysis. No statistically significant difference in fracture resistance was observed among the tested groups. Regarding the mode of failure, irreparable failure was significantly dominant, with no significant difference among the groups. Employing injectable restorative materials for cervical margin relocation had no detrimental effect on the fracture resistance of molars receiving nanoceramic resin-based CAD/CAM onlay restorations. CAD/CAM onlay restorations preceded by cervical margin relocation using injectable restorative materials could tolerate compressive loading comparably to those without cervical margin relocation.

On the drawability prediction of AA5754 aluminum alloy sheet

In order to study the drawability of AA5754 aluminum alloy blank, the numerical predictions of fracture failure behavior caused by cup drawing of metal sheet were carried out by using the GTN model and the thermodynamic-based continuous damage mechanics (CDM) model. The CDM model coupling the nonlinear isotropic and kinematic hardening laws with the isotropic ductile damage model was developed to carry out the numerical computation in the form of the user material subroutines. Although the forming limit curves predicted by GTN model and CDM model are distinctly different, but both of them are feasible to characterize the formability of metal sheets. The numerically predicted drawability of metal sheet is in good agreement with the experimental results in terms of strokes, sheet thinning and fracture failure location. The effects of sheet original thickness and friction coefficient between punch and sheet on the drawability of metal sheet were further investigated in detail.

Design and mechanical properties analysis of drill pipe’s joint thread with unequal taper under complex loads

The design of drill pipe joint thread with unequal taper is proposed to investigate the fracture failure of the API NC38 used in the drill pipe joint of the SU36-8-4H2 well. The effect of changes in thread taper on the stress distribution and mechanical properties of drill pipe joints is analyzed and compared with the API standard thread to determine the optimal thread structure with unequal taper. The results reveal highly concentrated stress at the last engaged thread root of API NC38 single-shoulder thread (SUT) may cause early yield failure of the joint threads. Adjusting the unequal taper of the pin thread mitigates uneven stress distribution in NC38 single and double-shoulder threads and enhances connection strength, particularly for SUT-II and DUT-I. However, altering the box thread’s unequal taper modifies the stress concentration slightly in NC38 single and double-shoulder threads. This offers limited tensile and compressive strength improvement. The maximum Mises stress value of SUT-II is reduced by 56.69% compared to SUT. The maximum Mises stress value of DUT-I is reduced by 34.87% compared to NC38 double-shoulder joint thread (DUT). This design approach can guide the optimization of other API threads and enhance joint strength for non-API and specialized taper threads.

From Ductile to Brittle: Defect-Engineered Mechanical Properties of Metal-Organic Frameworks.

The introduction of defects in metal-organic frameworks (MOFs) is an effective method to improve the performance of MOFs in many applications, but it also compromises the mechanical properties of MOFs. Thus, a comprehensive understanding of the mechanical properties of defective MOFs becomes important for the defect engineering in MOFs. Herein, using the in situ compression tests, we directly observe very different mechanical responses in HKUST-1 MOFs with various defect concentrations. The elastic-plastic deformation followed by a ductile flattened failure is found in the defective HKUST-1 with a small defect concentration, while a hyperelastic-plastic behavior accompanied by the brittle fracture failure could occur in the HKUST-1 with a large defect concentration. The strong dependence of deformation and failure behaviors of defective HKUST-1 crystals on the defect concentration is ascribed to the change in their local deformation mechanism and stress distribution with varying defect concentration, according to the analysis by finite element and molecular dynamics (MD) simulations. Our compression experiments and MD simulations also indicate a significant reduction in both Young's modulus and yield strength of HKUST-1 with growing defect concentration, which agrees well with the theoretical predictions of micromechanics theory. This study is expected to provide a more precise understanding of the mechanical properties of defective MOFs.

Editorial: Special Issue on Fatigue and Fracture Mechanics

Abstract The study of fatigue and fracture behaviors in engineered components remains a critical area across multiple disciplines. Limits on materials behavior are among the most significant technical challenges to enhancing the safety and reliability of engineering systems. Thus, accurately defining recent advancements in analytical methods and testing techniques within fatigue and fracture mechanics for engineered structures, components, and materials is essential. This analysis encompasses both experimental research and recent developments in modeling approaches. Key areas of interest include applications of emerging analytical tools and novel experimental techniques to assess and improve durability and damage tolerance using multiscale or multiphysics-based approaches; studies on the effects of additive manufacturing processes on fatigue and fracture properties; and implications of improved modeling and experimental capabilities on fatigue life forecasting and structural health monitoring strategies. In this context, a special issue in Materials Performance and Characterization offers readers valuable insights for their research. The call for papers attracted high-quality contributions from leading scientists and engineers resulting in 11 full-length manuscripts. The main topics covered include fatigue crack growth fracture, propagation, toughness fatigue, and damage failure inspection repair. The editorial teams extend their heartfelt thanks to the authors and reviewers for their dedication and to the ASTM staff for their support in bringing this issue to publication. We hope these papers provide valuable contributions to ongoing research efforts in fatigue and fracture mechanics.

Stress‐Based Fracture Model to Describe Ductile Fracture Behavior in Various Stress States

ABSTRACTBeing aimed at the strain path–related ductile fracture characteristic, this research develops a two‐component stress‐based DF2016 fracture model with 10 parameters through combining two single‐component corresponding fracture model with the addition form. This model possesses high flexibility to describe the ductile fracture behavior in various stress states. Stress‐based fracture‐related variables of the specimens with 10 different structures for WE43 alloy are captured, and the hardening behavior is with some strength differential effect. These fracture stresses have a strong sensitiveness to stress triaxiality and Lode parameter. Fracture loci of WE43 alloy are constructed by the proposed model with the smaller prediction error of 0.25683 than the stress‐based DF2016 fracture model (0.527). The reliability and high flexibility of the developed model are further uncovered through the description of ductile fracture behavior of AA2024‐T351 alloy. This research provides a valuable tool for predicting fracture failure of metals in engineering applications.

Study on Mode I Fracture Characteristics and Fracture Surface Morphology of Concrete–Sandstone Under Different Loading Rates

ABSTRACTThis paper studies the effect of various loading rates (0.02, 0.05, 0.5, and 1 mm/min) on the fracture characteristics of Mode I concrete–rock composites. Digital image correlation (DIC) and acoustic emission (AE) techniques are used to analyze cracked straight‐through Brazilian discs (CSTBD). Significant changes in Shannon entropy were observed before fracture failure, suggesting it as a reliable precursor indicator. The study found that as loading rates increased, the time for CSTBD to undergo plastic deformation decreased, leading to more transgranular and intergranular fractures. Surface morphology analysis revealed that fractal dimensions and surface roughness (Rrms) increased with higher loading rates. A MATLAB program, using power spectral density (PSD) to evaluate the joint roughness coefficient (JRC), demonstrated greater efficiency and accuracy compared with traditional visual assessment methods. This highlights the PSD method's superior performance in determining JRC values.

Crack Propagation and Fatigue Life Analysis of Wind Turbine Blades

This dissertation investigates the fatigue and fracture behaviour of wind turbine blades exposed to varying wind speeds and load intensities, aiming to enhance their durability and operational lifespan in sustainable energy systems. The increasing reliance on wind energy underscores the need for durable blades that can withstand cyclic loads and extreme environmental conditions, as fatigue and fracture failures significantly impact maintenance costs and reliability. This research specifically examines fatigue life and fracture initiation at wind speeds of 15 m/s and 60 m/s, analysing the effects of increased load intensities (30 MPa and 62 MPa). Finite Element Analysis (FEA) through ANSYS is employed to model fatigue and fracture dynamics, incorporating fatigue life prediction using S-N curves, stress analysis with von Mises stress, and crack propagation simulation via fracture mechanics principles, such as Paris’ Law. Results reveal a notable reduction in fatigue life with increased loads, evidenced by a drop from 9e09 to 7.9e08 cycles at 15 m/s, with comparable fatigue cycle reductions at 60 m/s. Fracture analysis identifies critical crack initiation points in high-stress areas, and simulations indicate the progressive nature of crack propagation under cyclic loads. These findings underscore the importance of integrating fatigue and fracture assessments in the design and maintenance strategies of wind turbine blades to enhance resilience and support the sustainable advancement of wind energy systems.

Fracture failure behavior of Al2O3 fabric under the combined interaction of high-temperature heat flow and tensile load

Fracture failure behavior of Al2O3 fabric under the combined interaction of high-temperature heat flow and tensile load