Internal Fracture Research Articles

Numerical investigation on the fracture and mechanical behaviors of marble containing two parallel fissures under triaxial compression conditions using FDEM

This paper aims to investigate the fracture and mechanical behaviors of fissured marble under triaxial compression. The two-dimensional models of marble with two parallel fissures and various rock bridge angles were established, and then the numerical simulations considering the effect of confining pressure were performed with the finite-discrete element method. The brittle-ductile transition and stress multi-peak characteristics are presented with the increase of the confining pressure. The characteristic strain, stress, and elastic strain energy exhibit various trends with the increment of the rock bridge angle, whilst increasing trend with the increment of the confining pressure. The cohesion presents the variation of first increasing and then decreasing with the increase of the rock bridge angle, and the friction angle presents the opposite trend to the cohesion. The proposed strength model can reflect the evolutions of the cohesion and the friction angle considering the effect of confining pressure and rock bridge angle. The elastic strain energy has the trends of nonlinear increase and fluctuation in the pre-peak and post-peak phases, respectively. The variation of kinetic energy is induced by the internal local fracture during the progressive failure. The failure pattern transforms from the tensile failure to the shear failure with the increase of the confining pressure. The coalescence behavior of cracks at the rock bridge can be classified into four modes.

Rock fractures developed in the Class II post-peak unloading

In this study, post-peak tests were conducted on sandstone specimens subjected to uniaxial compression under two different loading conditions: axial strain control and lateral strain control. The fractures developed in both loading regimes were investigated. Under axial strain control, Class I post-peak stress–strain curves (with negative slope) were obtained until the complete failure of the specimens. The observed macroscopic fractures have mixed orientations: sub-parallel and inclined to the axial loading direction. Under lateral strain control, the specimens were tested until different residual post-peak stresses; the tests yielded consistent Class II post-peak stress–strain curves (with positive slope). Interestingly, the tested specimens were found to be relatively intact, with only non-penetrating fractures observed on the lateral surfaces. X-ray CT scanning revealed that the subvertical macroscopic fractures were developed close to the lateral surfaces of the specimens in the post-peak stages, while the internal central parts remained visually undamaged. Analysis of longitudinal and shear wave velocities measured in the axial direction of sandstone specimens before and after post-peak tests under lateral strain control provided evidence of internal fracture (crack) development parallel to the loading axis in the internal central parts of the tested specimens. Concentration of these small fractures (cracks) is high, but it only marginally increases as the loading proceeds in post-peak region from 90% to 70% of the peak stress. This suggests that the Class II post-peak regime obtained under lateral strain control cannot be explained by pure unloading; also, the Class II post-peak unloading is mainly produced by the development of the large subvertical tensile fractures identified in the CT scans, rather than by the growth of these small fractures (cracks).

Research on calculation model for ultimate bearing capacity of tensile type anchor cables and the shape of internal fracture surface in anchorage segment

AbstractThe generalized model and parameter equation for the internal fracture surface of tensile type anchor cable anchorage section are constructed, and the calculation model of ultimate bearing capacity is derived based on the principle of limit equilibrium. The shape of the internal fracture surface in the anchorage section and the expression of its parameter equation are experimentally studied, and the variation law of the parameter equation and fracture range with the diameter of the anchor cable and confining pressure is analyzed. The parameter equation is substituted into the calculation model to realize the calculation and verification of the model. Through theoretical derivation, a calculation model of ultimate bearing capacity of anchor cable is obtained, which comprehensively considers the average shear strength of anchorage section, the shape of fracture surface, fracture range and confining pressure. The tests show that according to the magnitude of the confining pressure on the anchorage section, the internal fracture surface takes on two shapes: cylindrical and trumpet‐shaped, the parameter equation of trumpet‐shaped fracture surface obeys logarithmic distribution approximately. The coefficient a decreases with the increase of confining pressure but increases with the increase of anchor cable diameter, the constant b increases with the increase of confining pressure but decreases with the increase of anchor cable diameter. The ranges of horizontal and vertical fracture decrease with the increase of confining pressure, and increase with the increase of anchor cable diameter. The deviations between the theoretical calculation and the experimental results are less than 6.5%.

Analysis of the Influence of Shell Sand Content on the Performance of Ceramisite Lightweight Aggregate Concrete

This study investigates the impact of varying shell sand replacement rates (0%, 5%, 10%, 15%, 20%, 25%) on the properties of clay ceramsite lightweight aggregate concrete (CLC) through six experimental groups. Results indicate that a 5% replacement rate of shell sand yields optimal mechanical properties and working performance in CLC. Examination of specimen failure diagrams, electron microscopy and theoretical analysis reveals that shell sand predominantly influences CLC’s overall performance by influencing internal pore development and the formation of a “bonding defect zone” between shell sand and cementitious material. This also elucidates why specimen failure predominantly arises from internal ceramic particle fracture.

Failure analysis of strain clamps on a ± 800 kV transmission line

During X-ray testing of a ± 800 kV ultra-high voltage direct current transmission line tension clamp, it was found that the internal steel core had broken. To investigate the cause of the steel core fracture, the failed clamp was dissected and analyzed, including chemical material testing, mechanical performance testing, fracture morphology inspection, and analysis of the compression process of the tension clamp. A preliminary judgment was proposed on the cause of the internal steel core fracture of the tension clamp, And verification experiments and simulation analysis were conducted to preliminarily determine the cause of the steel core fracture, and it was ultimately concluded that the main reason for the steel core fracture was the incorrect compression sequence of the large cross-section wire tension clamp.

Definitive internal fracture fixation followed by staged free flap coverage (“fix followed by flap” protocol) for open Gustilo type IIIB fractures

BackgroundAlthough the concept of the “fix and flap” approach, in which definitive fracture fixation and flap coverage are completed in a single procedure at the earliest opportunity may seem ideal for the treatment of Gustilo type IIIB open fractures, the individual circumstances of patients, such as polytrauma or multiple fracture cases may not allow for the immediate fracture fixation and flap coverage (“fix and flap” approach). In our hospital, patients with Gustilo type IIIB open fractures are treated with definitive internal fixation of the fracture followed by staged flap coverage (“fix followed by flap” protocol) when the “fix and flap” approach was not feasible due to the patient's condition or difficulty in coordinating surgery schedules. The “fix followed by flap” protocol provides benefits in terms of flexibility in adjusting the surgical timetable, simplifying the planning of flap coverage following fracture fixation, and minimizing individual surgical invasion. MethodsWe reviewed 10 cases of severe open fractures treated with the “fix followed by flap” protocol and evaluated their outcomes. All surgical procedures, including wound debridement, fracture fixation, and flap coverage, were performed by orthoplastic surgeons specializing in both fracture surgery and microsurgery including soft tissue reconstruction. ResultsAll free flaps survived, and no partial necrosis was observed. None of the patients developed postoperative deep infection up to the last follow-up. Fracture union was achieved in all patients with or without autologous bone grafts. The median time for union was 9.4 months (range, 4–12 months). ConclusionsThis study presents favorable outcomes of treatment for Gustilo type IIIB open fractures with fracture fixation followed by staged flap coverage (“fix followed by flap” protocol). Despite a delay in flap coverage, the consistency of treatment provided by orthoplastic surgeons may have contributed to the favorable outcomes in this study.

Anti-penetration response and response mechanism of laminated structures made of different composite materials under impact load

Composite laminated structures are often subjected to high-speed impact from external objects in high impact environments, resulting in unpredictable forms of damage and even uncontrollable damage modes. To ensure the safety and reliability of these structures, research was conducted on the anti-penetration response and response mechanism of laminated structures made of different composite materials. Using carbon fiber reinforced plastic (CFRP) laminated structures and glass fiber/epoxy resin composite aluminum alloy (GLARE) laminated structures as research objects, a high-impact experimental setup was constructed based on a first-stage light gas gun to explore the relationship between the energy absorption characteristics and impact energy of composite laminates. Combined with the ballistic limit equations, the ballistic limit values of the composite laminated structures were determined, and the ballistic limits of the 2 mm thick CFRP laminated structure and the 2 mm thick GLARE laminated structure were 138.3 m/s and 215.6 m/s, respectively. The damage modes of CFRP laminated structure are mainly fiber fracture on the impact surface and fiber delamination, fiber tensile fracture and fiber bundle splitting on the back surface, while the damage modes of GLARE laminated structure are mainly plastic deformation, internal fiber fracture and crack extension at the penetration. At the same time, the cohesion unit is introduced to carry out numerical simulation research, which shows that the damage pore morphology of the cohesion unit between layers of composite laminated structures are closely related to their fiber layups, and the damage mode of cohesion unit between layers of composite laminated structures have been investigated, which reveals the damage mechanism in high-impact environments. The research results provide theoretical basis and common technical support for reverse design of composite laminated structures suitable for high impact environments.

Numerical evaluation of the internal fracture mechanism of the single PBL shear connector considering the effects of position and strength of the transverse rebar

AbstractThe perfobond (PBL) shear connector reinforced with transverse rebar effectively contributes to sufficient ductility, bearing capacity, and anti‐fatigue behavior to hybrid structures. The construction practice involves the placement of the transverse rebar at the bottom position within the concrete dowel, whereas past studies employed transverse rebar in the center of the dowel; hence, there exists a gap between literature and design practices. Furthermore, there is no specific information in the design guidelines for hybrid structures on the influence of the position of the transverse rebar. Therefore, the current research deals with the analytical investigations employing the coupled Rigid Body Spring Model (RBSM) and the nonlinear solid Finite Element Method (FEM) that encompass the internal fracture behavior of concrete with the various parameters of transverse rebar, particularly the position and strength, to recognize the failure mechanism. It was determined that the numerical model accurately captured the test shear capacity and failure modes. The internal failure process of a specimen with transverse rebar at the bottom position, identical to actual field practice, revealed that as the height of the concrete region above the rebar rises, more compressive stresses in a trapezoidal manner are being generated, leading to an enhancement of the deformation capacity. Furthermore, it was confirmed that the specimen with the transverse rebar inserted at the bottom generates the greatest axial force, which is followed by the greatest shear capacity.

Effect of electrochemical charging on the hydrogen embrittlement susceptibility of a low-alloyed tempered martensitic steel submitted to high internal pressure

The influence of hydrogen on the mechanical behavior of a quenched and tempered 42CrMo4 steel has been evaluated by means of high internal pressure fracture tests carried out on hydrogen precharged notched cylindrical specimens. The notched cylindrical specimens were precharged for 3 h time with 1.2 mA/cm2 in two different aqueous media: 1 M H2SO4 added with 0.25 g/l As2O3 and 3.5% of NaCl solution. Hydraulic fracture tests were performed at different ramps of pressure: 7000, 220, 80, 60 and 30 MPa/h, respectively. Hydrogen damage was more marked when the acid aqueous medium (1 M H2SO4 + 0.25 g/l As2O3) was employed. In this case, a higher hydrogen concentration was introduced, leading to hydrogen decohesion micromechanisms (HEDE) near the notched region, especially when tests were performed at 60 MPa/h. Hydrogen embrittlement susceptibility is discussed in terms of the microstructural singularities and the operative fracture micromechanisms observed in each case.

Open reduction and internal fixation in treatment of four cases of bipolar clavicle dislocations

To summarize the method and effectiveness of open reduction and internal fixation in the treatment of 4 cases of bipolar clavicle dislocations. Between June 2017 and June 2022, 4 patients with bipolar clavicle dislocations were admitted. There were 3 males and 1 female. The age ranged from 27 to 63 years, with an average age of 45 years. There were 2 cases of crushing injury of mine car, 1 case of traffic accident injury, and 1 case of heavy object injury. The time from injury to operation was 3-7 days, with an average of 5.0 days. The sternoclavicular joint dislocations were classified as Grade Ⅱ in 1 case and type Ⅲ in 3 cases, and anterior dislocation in 3 cases and posterior dislocation in 1 case. The acromioclavicular joint dislocations were classified as Tossy type Ⅱ in 2 cases and type Ⅲ in 2 cases. After open reduction, the sternoclavicular joint and acromioclavicular joint were fixed with lateral malleolus locking titanium plate and clavicular hook plate, respectively. All operations were successfully completed without vascular or nerve injury. All incisions healed by first intention. All patients were followed up 12-18 months, with an average of 14 months. At last follow-up, the shoulder joint functions were rated as excellent in 3 cases and good in 1 case according to Rockwood score. During follow-up, there was no loosening of internal fixator or fracture. The internal fixators were removed in all patients at 5-7 months after operation (mean, 6 months), and no re-dislocation occurred after removal. For bipolar clavicle dislocation, open reduction combined with lateral malleolus locking titanium plate fixation of the sternoclavicular joint and clavicle hook plate fixation of the acromioclavicular joint can achieve good effectiveness. It has the advantages of simple operation, high safety, firm fixation, and fewer complications, and the shoulder function recovers well.

Patient-Specific Implant Customization for Treatment of Internal Orbital Fractures Using Office-Based Three-Dimensional Printing.

Three-dimensional (3D) modeling technology aids the reconstructive surgeon in designing and tailoring individualized implants for the reconstruction of complex craniofacial fractures. Three-dimensional modeling and printing have traditionally been outsourced to commercial vendors but can now be incorporated into both private and academic craniomaxillofacial practices. The goal of this report is to present a low-cost, standardized office-based workflow for restoring bony orbital volume in traumatic orbital fractures. Patients with internal orbital fractures requiring open repair were identified. After the virtual 3D models were created by iPlan 3.0 Cranial CMF software (Brainlab), the models were printed using an office-based 3D printer to shape and modify orbital plates to correctly fit the fracture defect. The accuracy of the anatomic reduction and the restored bony orbital volume measurements were determined using postoperative computed tomography images and iPlan software. Nine patients fulfilled the inclusion criteria: 8 patients had unilateral fractures and 1 patient had bilateral fractures. Average image processing and print time were 1.5 hours and 3 hours, respectively. The cost of the 3D printer was $2500 and the average material cost to print a single orbital model was $2. When compared with the uninjured side, the mean preoperative orbital volume increase and percent difference were 2.7 ± 1.3mL and 10.9 ± 5.3%, respectively. Postoperative absolute volume and percent volume difference between the orbits were -0.2 ± 0.4mL and -0.8 ± 1.7%, respectively. Office-based 3D printing can be routinely used in the repair of internal orbital fractures in an efficient and cost-effective manner to design the implant with satisfactory patient outcomes.

Microscopic fractures shown inside tablets after impact

In prior work, rough handling of oral tablets had been observed to drastically speed up their disintegration in water. The purpose of this study was to confirm or refute that the formation of internal microscopic fractures during rough handling is the underlying mechanism. Impacted and control tablets were subjected to micro-computed tomography and to brightness-mode ultrasound. The former revealed fracturing with a maximum crack width of 14 μm. The latter revealed strong acoustic response from the internal structure of the impacted tablets. These results confirm the hypothesis. Disintegration speed is used as a quality control mechanism after tablet manufacturing and transportation.

Mechanical performance and failure mechanism of U-steel support structure under blast loading

The U-steel support structures of underground caverns are prone to instability and failure under blast loads. The purpose of the underground cavern reinforcement is to mobilise the self-supporting capacity of the surrounding rock to resist the blast. To better understand the mechanical performance and failure mechanism of the U-steel support, the fracture process and vibration behaviour of the support structure under blast loading are investigated by the microseismic monitoring experiment. The dynamic responses of the cavern support structures under blast loading are investigated, and the potentially hazardous sections of the U-steel support structure are revealed by the theoretical analysis. The microseismic monitoring results show that the blast induced microseismic events are concentrated in the arch shoulder of the small chainage, correspondingly the U-steel structures in this region have been partially extruded and deformed. The failure mechanism of the supporting structure is presented. In order to effectively inhibit the internal fracture evolution or macroscopic failure of the rock mass, the synergetic reinforcement scheme of the structures is proposed. The results of the research can be used as a reference for the design and control method of the U-steel support in similar projects.

Prevalence of Craniofacial Injuries in the Elderly Population.

Recognizing and understanding risk factors for craniofacial injury in the elderly is of paramount importance in prevention. This research aims to investigate the prevalence of craniofacial injuries in connection with extrinsic preventable factors, particularly identifying common household products that pose the greatest risk for such injuries. This study was done with the utilization of the 2013 to 2022 National Electronic Injury Surveillance System (NEISS). Data gathered included patient age, injury type, cause of injury, and year of incidence. "Elderly" was defined as an individual of 65 years of age or older. There was a total of 9,703,688 estimated national cases of elderly craniofacial injury from 2013 to 2022. In all, 5,888,112 (60.68%) of these occurred in females. In descending order, the 5 most common items responsible for craniofacial injury in the elderly are floors/flooring Materials (3,741,706, 30.92%), beds/bed frames (1,250,396, 10.33%), stairs/steps (907,92, 7.50%), chairs (546,697, 4.52%), and tables (453,989, 3.75%). These top 5 account for roughly 57% of all cases. The 5 most common presenting diagnoses were internal injury (2,957,095, 40.21%), lacerations (1,435,926, 19.53%), ABR (1,191,008, 16.20%), fracture (568,842, 7.74%), and hematoma (355,871, 4.84%). Out of the roughly 10 million cases of craniofacial injury in the last decade, ~three-fifths have happened to women. The majority of injuries occur in a home setting. The overwhelming majority of cases were related to the product code 1807-floors or flooring materials, and the largest diagnosis was internal injury by a wide margin. Evidently, there is a large population of elderly patients who suffer from craniofacial injuries related to objects and items that permeate within their living residences. The elimination of excess elderly craniofacial injury can be achieved by reducing fall risk factors in the immediate vicinity of the elderly.

Three-Dimensional Optical Imaging of Internal Deformations in Polymeric Microscale Mechanical Metamaterials.

Recent advances in two-photon polymerization fabrication processes are paving the way to creating macroscopic metamaterials with microscale architectures, which exhibit mechanical properties superior to their bulk material counterparts. These metamaterials typically feature lightweight, complex patterns such as lattice or minimal surface structures. Conventional tools for investigating these microscale structures, such as scanning electron microscopy, cannot easily probe the internal features of these structures, which are critical for a comprehensive assessment of their mechanical behavior. In turn, we demonstrate an optical confocal microscopy-based approach that allows for high-resolution optical imaging of internal deformations and fracture processes in microscale metamaterials under mechanical load. We validate this technique by investigating an exemplary metamaterial lattice structure of 80 × 80 × 80 μm3 in size. This technique can be extended to other metamaterial systems and holds significant promise to enhance our understanding of their real-world performance under loading conditions.

Mechanical behavior, acoustic emission and principal strain field evolution properties of layered cemented paste backfill under unconfined compression

In order to save costs, the layered filling method is adopted by mine enterprise to fill the underground goafs. To understand the mechanical behavior, damage evolution and failure modes the layered cemented paste backfill (LCPB), this study investigated the strength properties, acoustic emission (AE) characteristics and principal strain field evolution of LCPB samples with cement-to-tailings (c/t) ratio of 1:4, 1:6, 1:8, 1:10, and the height (h) of middle layer of 30 mm, 35 mm, 40 mm, 45 mm, 50 mm. The obtained results indicate that: (1) UCS of LCPB decreases with the increases of h and with the decreases of c/t ratio. The influence of c/t ratio on UCS of LCPB is in a good agreement with logarithmic function, while the variation relationship between h and UCS of LCPB satisfies the exponential function. (2) The acoustic emission signals first appeared during the transition from the compression to the elastic stage, reaching a maximum approaching the peak stress, and AE ringing counts also appeared during the post-peak stage. Internal fracture type of LCPB under external loading is a tension-shear composite fracture dominated by shear fracture. (3) The damage of LCPB occurs mainly in the middle layer and then extends to the upper and lower layer with the formation of visible localized zones. The damage of LCPB developed from significant shear damage to tensile-shear damage with the decreased of the c/t ratio, and transitioned from tensile-shear damage to complex damage dominated by shear damage and supplemented by tensile damage as h increased. Ultimately, the findings of this work can provide a reference for the design of LCPB.

Evolution characteristics of fracture volume and acoustic emission entropy of monzogranite under cyclic loading

The volume evolution behavior of rock fissures and the characteristics of acoustic emission under cyclic loading are critical for rock stability analysis. To study the volume change behavior of monzogranite fissures and the characteristics of acoustic emission signals under cyclic loading, we selected samples of monzogranite at − 1600 m from a gold mine located in the Jiaodong Peninsula at a depth of − 1600 m and investigated the samples using triaxial cyclic loading—unloading tests and acoustic emission monitoring. As the volume change behavior of the monzogranite fissures and acoustic emission signals were monitored and recorded, the calculated fracture volume strain ratio coefficient and acoustic emission entropy value were proposed to describe the evolution process of fissures inside the rock. The research results showed that the volume strain ratio curve of the rock fractures exhibited a logarithmic variation characteristic during the cyclic loading and unloading, and the fracture volume strain ratio better reflected the relative scale of the internal fracture strain in the rock to the total volume strain. The acoustic emission entropy value reflected the crack evolution behavior during the loading and failure processes, which was a rapid decline in the initial stage of loading and a rapid upward trend in the failure stage. The observed “V”-shaped change in the acoustic emission entropy can be used as an early warning for rock failure. The research results can provide theoretical guidance for rock stability analysis.

Epidemiology of work-related fall injuries resulting in hospitalisation: individual and work risk factors and severity

ObjectivesInjuries at work are common and costly for individuals and employers. A common mechanism of workplace injury is through falls, but there have been few epidemiological studies of risk factors....

High-Temperature Oxidation Resistance and Molten Salt Corrosion Study of YSZ, CeYSZ, and YSZ/CeYSZ Thermal Barrier Coatings by Atmospheric Plasma Spraying

Five thermal barrier coatings (TBCs), namely TBC-1 (YSZ), TBC-2 (CeYSZ), TBC-3 (YSZ:CeYSZ = 1:2), TBC-4 (YSZ:CeYSZ = 1:1), and TBC-5 (YSZ:CeYSZ = 2:1), were fabricated using the atmospheric plasma spraying (APS) method. Their oxidation behaviors at 1100 °C and corrosion resistance to molten salts (V2O5 + Na2SO4) at 900 °C were examined. After 100 h of oxidation, the thermally grown oxide layer (TGO) for YSZ primarily contained Cr and Ni oxides with significant internal fractures, presenting a continuous band-like Al2O3. In dual-ceramic configurations, an increase in CeYSZ thickness led to a rise in Al content and reduced Cr and Ni in TGO, with the surface fracture morphing into an internal porosity. Following salt corrosion, YSZ revealed rod-like YVO4 and m-ZrO2 as corrosion products, whereas CeYSZ displayed chain-structured CeO2, CeYO4, and YVO4 combined with m-ZrO2. YSZ coatings underwent notable phase transitions with evident densification, forming a corrosion layer of approximately 10 μm. Conversely, CeYSZ showed a limited phase change, retaining porosity without a distinguishable corrosion layer. As CeYSZ thickness increased from 100 μm to 200 μm in the dual-ceramic structure, salt penetration reduced. Evidently, the dense structure of CeYSZ heightened diffusion resistance against oxygen and corrosive salts, rendering superior oxidation and corrosion resistance over YSZ. By optimizing the thickness ratio between CeYSZ and YSZ, whilst retaining total ceramic layer thickness, the dual-ceramic TBC’s resistance to high-temperature oxidation and corrosion can be enhanced.

Effect of Predamage on the Fracture Energy of Double-Network Hydrogels.

Double-network (DN) hydrogels are tough soft materials, and the high fracture resistance can be attributed to the formation of a large damage zone (internal fracture of the brittle first network) around the crack tip. In this work, we studied the effect of predamage in the brittle network on the fracture energy Γc of DN hydrogels. The prestretch of the first network was induced by prestretching the DN gels to prestretch ratio λpre. Depending on the λpre in relative to the yielding stretch ratio λy, above which the brittle first network starts to break into discontinuous fragments inside DN gels, two regimes were observed: Γc decreases monotonically with λpre in the regime of λpre < λy, mainly due to the decreasing contribution from the bulk internal damage, while Γc increases with λpre in the regime of λpre > λy. The latter can be understood by the release of the hidden length of the stretchable network strands by the rupture of the brittle network, whereby the broken fragments of the brittle network could serve as sliding cross-links to further delocalize the stress-concentration near the crack tip and prevent chain scissions.