Areas Of High Stress Research Articles

Impact of Plate Thickness and Joint Geometry on Residual Stresses in 347H Stainless Steel Welds

Weldments of 347H stainless steel are potentially susceptible to stress relaxation cracking at elevated service temperatures. Mitigation of stress relaxation cracking susceptibility within a multipass weld requires a good understanding of welding practices and manufacturing techniques to control high tensile residual stresses. In this work, the dependence of residual stress distribution in 347H stainless steel on base plate thickness, joint geometry design, and preheating condition was systematically investigated by using three-dimensional finite element models. The finite element models were validated through good agreement between neutron diffraction measurements and calculated elastic strains. The single-V-groove welds with and without a preheating step all produced similar peak von Mises residual stresses, above 450 MPa, within both the fusion zone and heat-affected zone (HAZ). In plates thicker than 0.5 in. (12.7 mm), high tensile residual stress could be observed in a relatively large area, from the middle of the plate thickness to underneath the top surface. A double-V groove shifted the high tensile stress area to the middle thickness of the weld. A single-J-groove weld was able to confine the residual stress to a very small region near the middle thickness within the fusion zone and suppressed the von Mises residual stress within the HAZ to below 400 MPa.

A novel asymmetric stress unloading technology in two sides of coal roadway in deep mine: A case study

The existing stress unloading technology using dense equal-diameter large drilling usually results in damaging the load-bearing structure of the shallow surrounding rock of the roadway. Therefore, this study, while providing full anchor cable strong anchorage support for the roadway sides, proposes an asymmetric stress unloading technology on the two sides of a coal roadway. Small-diameter holes are directly drilled in the shallow low-stress area, and the large-diameter stress unloading hole (LSUH) is excavated in the deep stress concentration peak area for the right side of the roadway; utilizing the floor rock roadway, by drilling upward through the rock stratum, excavating the LSUH in the deep stress concentration peak area for the left side of the roadway. Full anchor cable reinforcement technology for the shallow surrounding rock of roadway sides forms a thick layer anchorage load-bearing structure, avoiding cracks further development of the shallow coal seam of the roadway side and creating a quality stress environment for the implementation of the LSUH in the deep area of the roadway side. The small drilling and the coal slag discharge of the roadway left side does not pass through the shallow anchorage area of the roadway left side, and the shallow small drilling on the roadway right side is supported reinforcement by the steel pipe, which minimize the impact of hole-manufacturing on the shallow anchorage area to the greatest extent possible. Large-diameter weak structural stress unloading holes are arranged in the deep stress concentration peak area of far away from anchorage area of the roadway side, making the high concentration stress areas around the roadway be transferred to deeper area without affect the stability of the shallow anchorage area, also making the plastic deformation of the surrounding rock in the stress concentration area of the roadway side be transferred to the weak structural area of the stress unloading holes. A numerical model for the asymmetric stress unloading technology on the two sides of a coal roadway is established to investigate the influence of different stress unloading parameters on the roadway side stress. Engineering practice shows that this technology can ensure the long-term stability of the roadway.

A Newborn Screening Program for Sickle Cell Disease in Murcia (Spain).

Sickle cell disease (SCD) is an inherited autosomal recessive hemoglobin disorder caused by the presence of hemoglobin S, a mutant abnormal hemoglobin caused by a nucleotide change in codon 6 of the β-globin chain gene. SCD involves a chronic inflammatory state, exacerbated during vaso-occlusive crises, which leads to end-organ damage that occurs throughout the lifespan. SCD is associated with premature mortality in the first years of life. The process of sickling provokes asplenia in the first years of life with an increased risk of infection by encapsulated germs. These complications can be life-threatening and require early diagnosis and management. The most important interventions recommend an early diagnosis of SCD to ensure that affected newborns receive immediate care to reduce mortality and morbidity. The newborn screening program in the region of Murcia for SCD began in March 2016. We aimed to determine the incidence of sickle cell anemia and other structural hemoglobinopathies in the neonatal population of the region of Murcia, an area of high migratory stress, and to systematically assess the benefit of newborn screening for SCD, leading to earlier treatment, as well as to offer genetic counseling to all carriers. The prevalence of SCD in our region is similar to others in Spain, except for Catalonia and Madrid. The newborns with confirmed diagnoses of SCD received early attention, and all the carriers received genetic counseling.

A comparison of the effects of incremental and snowplow techniques on the mechanical properties of composite restorations.

Glass fibre-reinforced composite (GFRC) has the potential to enhance the mechanical properties of resin-based restorations. Nevertheless, the application technique can influence the cervical margin porosity, potentially reducing the mechanical strength of restorations. In an in vitro setup, mould specimens underwent six different treatments to assess the effects of snowplow and incremental curing techniques on the properties of GFRC (EverX) and universal resin composite (Filtek). Mechanical properties, namely flexural strength (FS), compressive strength (CS) and Vickers hardness (VH), were evaluated following ISO 4049 standards. Data interpretation utilized the Kruskal-Wallis tests. No significant difference emerged across groups for FS. CS in the snowplow method with lesser EverX thickness (SnPl_1) was comparable with only EverX and Filtek (P > 0.05). The CS was reduced in the snowplow technique with greater EverX thickness (SnPl_2) (P < 0.05) and further decreased with the incremental method (P < 0.001). VH results showed that EverX Posterior was consistently softer than Filtek, with specific patterns of hardness variations among different application methods. Applying EverX and Filtek using the snowplow technique delivers superior CS and VH for restorations in contrast to the incremental method. Utilizing the snowplow approach in high-stress areas can make restorations more fracture-resistant.

A Phase-Field Discrete Element Method to study chemo-mechanical coupling in granular materials

Geochemical reactions are ubiquitous for subsurface energy extraction and storage applications, like geothermal electricity production or hydrogen storage, but also for other applications aiming at reducing climate change like underground CO2 disposals [1]. Those reactions lead to mineral dissolution/precipitation that can modify the different properties of the reservoir rock and the caprock. For example, porosity of the porous material depends strongly on the dissolution/precipitation of the solid phase. It can thus affect the evolution of its permeability, a key parameter for most of those applications that involve the transport of a fluid through the reservoir. Moreover, the mechanical behavior and rupture of geomaterials is also strongly affected by dissolution/precipitation phenomena. In the case of cemented rocks, debonding can occur during weathering and strongly weakens the material [2]. This strength degradation has also been highlighted during oedometric tests in the case of granular materials presenting no cohesion [3]. In the case of underground storage applications, if a strength reduction is induced in the caprock, cracks can be created, leading to a migration pathway and leakage. It can also affect the behavior of faults in the vicinity of the reservoir and induce earthquakes [4]&#x0D; Granular material (like in fault) or sedimentary rock can be modeled by the discrete element method (DEM). This method was first developed by Cundall and Strack to model the micromechanical behavior by reproducing more accurately the interactions in an assembly of grains. In the classical approach, grains are modeled as disks (2D) and spheres (3D), however, real particles can be highly irregular. These complex shapes of the grains influence greatly the macroscopic mechanical behavior of the material [5] and accurate models should aim at capturing this complexity. To do so, different approaches have been developed in the frame of DEM like particles cluster, ellipsoids, polygonal (2D) or polyhedral (3D) particles [6]. The latter is the most accurate solution, but it tends to overestimate the roundness of the particles and show some limitations to reproduce experimental results [7]. Recently, a level-set discrete element model was developed and allowed to capture the complex shape of the grains and reproduce experimental results [8].&#x0D; To model grain dissolution/precipitation, discrete elements are often considered with a homogenous decrease/increase of the particle diameter. But in some cases, like pressure-solution, the dissolution/precipitation are localized. Hence, the dissolution occurs in the high-stress area, whereas the precipitation occurs in the low-stress area with a large solute concentration. This diffusive mass transfer is done within the pore fluid. Considering the granular material as a phase, the phase-field theory (PF) is a good candidate to model with physics-based laws an addition or reduction of the quantity of material locally. The dissolution at the contact is controlled by the introduction of mechanical and chemical energy into the Allen-Cahn formulation on the phase variables, whereas the precipitation and the mass conservation are verified by a coupled diffusion formulation on the solute concentration.&#x0D; In this study, an extension to the discrete element method is developed to simulate the irregular shapes of particles in a granular material and their heterogeneous change using the phase-field variable as a particle’s geometrical descriptor. This method, available on https://github.com/AlexSacMorane/PFDEM_ACS_MultiGrains, is applied to reproduce results from previous experiments on K0 evolution [9]. The influence of the grain shape has been highlighted. Then, the model is used to investigate on the pressure-solution phenomenon at several grains level [10]. For example, a so-called Andrade creep law has been reproduced.&#x0D; In conclusion, this new framework enables us to model chemo-mechanical couplings, considering the true shape of the grain. It is used to investigate the influence of the different physical phenomena (dissolution, precipitation or diffusion) controlling the rate of material compaction and of the macro properties evolutions, as the porosity, permeability or strength.

Assessing a natural field of rock mass stress by means of in-situ measurements within Vostochnaya Sary-Oba deposit in Kazakhstan

Purpose is to assess a natural field of rock mass stress within Vostochnaya Sary-Oba deposit using in-situ measurements. It will help identify stress distribution as well as high-stress areas that may be dangerous for mining operations. Methods. The research has applied a technique of well hydraulic fracturing to study parameters of the initial stress field within the deposit. For the purpose, two metering points in two measuring (horizontal and vertical) wells were used. Hydraulic fracturing has been tested at each installation location. Findings. The in-situ measurement results have helped obtain quantitative parameters of stress-strain state of the rock mass. It has been understood that the available tectonic disturbances may result from the shape of structural folds as well as from tectonic fissility. Operating azimuth of the maximum horizontal stress within the points coincides, it is equal to 70° ± 10. Originality is the use of a new approach to assess the stress rock mass state within Vostochnaya Sary-Oba deposit while applying in-situ measurements and well hydraulic fracturing. The abovementioned favours more accurate and reliable assessment of rock stress state at the field being quite important for mining safety and for the development of the efficient supporting procedures and ore extraction procedures. Practical implications. The research results are applicable to adapt project documents for the deposit mining, a supporting technique selection, and ore extracting. Moreover, they will help make the substantiated choice of a structure and geotechnical parameters taking into consideration safety of operations as well as quality of ore mining. In addition, the results help develop measures to prevent rock mass outburst and fall in mine workings.

Orthodontic Internal Resorption Assessment in Periodontal Breakdown-A Finite Elements Analysis (Part II).

This finite elements analysis (FEA) assessed the accuracy of maximum shear stress criteria (Tresca) in the study of orthodontic internal surface resorption and the absorption-dissipation ability of dental tissues. The present study was conducted over eighty-one models totaling 324 simulations with various bone loss levels (0-8 mm), where 0.6 N and 1.2 N were applied in the intrusion, extrusion, rotation, tipping, and translation movements. Tresca criteria displayed localized high-stress areas prone to resorption for all situations, better visible in the dentine component. The internal resorptive risks are less than external ones, seeming to increase with the progression of the periodontal breakdown, especially after 4 mm. The internal and external surface high-stress areas are strictly correlated. The qualitative stress display for both forces was almost similar. The rotation and tipping displayed the highest resorptive risks for the pulp chamber, decreasing with bone loss. The resorptive risks seem to increase along with the progression of periodontal breakdown if the same applied force is kept. The dentine resemblance to ductile based on its high absorption-dissipation ability seems correct. Tresca seems to supply a better predictability of the prone-to-resorption areas than the other failure criteria.

Use of supplemental rod constructs in adult spinal deformity surgery

Operative treatment for adult spinal deformity (ASD) commonly involves long posterior instrumented fusions with primary rods spanning from the base of the construct to the upper instrumented vertebra. Over the past decade, additional supplemental rods have been increasingly utilized to bolster the primary instrumentation and mitigate risk of primary rod fracture/pseudarthrosis at areas of high biomechanical stress (e.g., 3-column osteotomy [3CO], multiple posterior column osteotomies [PCOs], lumbosacral junction). Supplemental rods for 3CO include satellite rods (4-rod technique with 2 deeply recessed short rods independently attached to pedicle screws across the 3CO), accessory rods (attached to primary rods via side-to-side connectors), and delta rods (accessory rods contoured only at the proximal and distal attachments to primary rods). Utilizing more than 4 rods across a 3CO may increase posterior construct stability; however, diminished load transfer to the anterior vertebral column may increase risk of nonunion and instrumentation failure. Similar supplemental rod constructs can be utilized to support multiple PCOs and/or the lumbosacral junction. We generally recommend using bilateral accessory rods for a total of 4 rods to support the lumbosacral junction (2 accessory rods and 2 primary rods). The novel “kickstand rod” can help facilitate coronal correction and/or function as an accessory rod distally anchored to an independent iliac screw; appropriate nomenclature is “iliac accessory rod” in cases without true kickstand distraction. In this narrative review, we aim to (1) provide a brief historical overview of supplemental rod constructs, (2) describe current indications for supplemental rods, and (3) report our results from a longitudinal analysis (2008–2020) of supplemental rod constructs used by International Spine Study Group (ISSG) surgeons.

Failure analysis of cold rotary swaging die

Failure analysis was carried out on a cold rotary swaging die for batch production of small shafts and tubes. Characteristics of top and bottom surfaces were examined. Hardness distribution on the cross section and microstructure were analyzed. Stress distribution and wear on the die during rotary swaging were investigated by finite element analysis (FEA). The study showed that the internal damage, phase inhomogeneity, concentrated forming stress were the main three reasons for premature failure of the die. The internal damage caused the tensile strength to reduce by more than 55%. The content of 33.55% martensite near the arc surface was not high enough to prevent the cracks from propagating inward. The stress concentration at the bottom of the arc surface further decreased the bearing ability. Increasing the fillet angle can decrease the high stress by around 60% at the transition area and improving surface design can disperse the high stress area while reducing maximum stress by more than 35%.

Parametric study on lateral behavior of totally precast RC shear wall with horizontal bolted connection

Dry-type connections have gained considerable popularity worldwide due to their superior construction efficiency and quality. However, a significant drawback of most conventional dry-type connections is the direct embedding of connectors in the concrete wall panel, consequently causing stress concentration in the connections and leading to extensive spalling of concrete. This study introduces an innovative high-strength bolted connection as a solution to address the problem of stress concentration in concrete. To evaluate the seismic performance of the high-strength bolted connection, monotonic lateral loading tests were conducted. In this study, a finite element (FE) model was developed using ABAQUS software, and validated through experimental results. Furthermore, a parametric study was conducted using the FE model to assess the influence of several key design parameters on the lateral response and anti-slip capacity of the bolted connection in the precast shear wall. These parameters include bolt specifications, anti-slip coefficient, flange thickness of the H-connector, widths of the initial gap, axial compression ratio, and connection arrangement. The results indicate that the anti-slip capacity is not significantly influenced by the flange thickness of H-connectors and initial gap width, but it increases with an increase in bolt specification, slip coefficient, and axial compression ratio. Additionally, the ultimate bearing capacity of the precast shear wall remains unaffected by both the anti-slip coefficient and the initial gap width. Moreover, the high-stress area of the H-connector is concentrated at the ends. Finally, the design parameters are recommended according to the numerical analysis results.

Study on Surface Deformation and Movement Caused by Deep Continuous Mining of Steeply Inclined Ore Bodies

In order to study the surface movement and deformation law of deep continuous mining of steeply inclined orebodies in high-stress areas, the surface movement and deformation law of deep continuous mining by caving method in the Shizishan mining area was studied based on the field fissures investigation, GPS monitoring, and large-scale geotechnical engineering numerical simulation software FLAC3D 5.0. The results show that with deep continuous mining of the orebody, surface fissures, and monitoring displacement are rapidly increasing. After the stoping of different sublevel orebodies, there will be an obvious settlement center on the surface, and the horizontal surface displacement also shows a trend of gradual increase. The results indicate that surface subsidence at the mine site is in an active development phase. The research results are of great significance to the prevention and control of surface rock movement disasters in mining areas.

Analysis of a stepped shaft in a rubber cracker machine

This paper presents a comprehensive failure analysis study of a stepped shaft in a rubber recycling factory. The investigation aims to identify the underlying cause of the shaft's failure and provide insights for enhancing the reliability and durability of industrial machinery. Through visual examination, scanning electron microscopy (SEM), mechanical characterization, elemental composition analysis using X-ray fluorescence (XRF), and finite element analysis (FEA), the study reveals the presence of low-cycle fatigue, primarily attributed to small surface imperfections. The macroscopic inspection indicates a high-stress concentration area where the shaft diameter changes. FEA results corroborate stress concentration in the failure region. Safety factor analysis suggests premature failure of the shaft. Further inspection reveals that misalignment of the shaft with respect to the ground leads to excessive vibration, potentially contributing to the low-cycle fatigue failure. To address this, a solution is proposed and implemented, involving correct alignment of a new shaft, reinforced fixation of the machine to the ground, and construction of a steel-reinforced concrete base. Subsequent operation of the rubber cracker machine with the implemented solution demonstrates successful prevention of shaft failures. The study highlights the importance of proper design, material selection, and operational considerations in enhancing the reliability of industrial machinery.

Change Characteristics of the Advance Stress and Strata Fracture Structure of Spatial Isolated Island Formed by Roof Drainage

Large-energy microseismic events, coal bursts, and other abnormal mine stress are often observed in spatial isolated island areas in the roof water-rich gob-side working face during mining operations. In view of this problem, numerical simulation and on-site microseismic monitoring are employed to study the advance abutment stress and strata fracture structure in the spatial island area formed by ‘roof drainage + goaf’ during mining and the method of eliminating the spatial island area. The results show that the lateral stress is distributed in a step-like pattern, and the drainage area and goaf are superimposed to form a high-stress space island area before the mining of the working face along the goaf. The distribution pattern of the advance abutment stress in the spatial island area changes from ‘C’ type to ‘S’ type during the mining process. The strata structure of the roof water-rich gob-side working face is either a single-peak arch or double-peak arch, and the arch peak corresponds to the boundary of the drainage area. The method of local hydraulic fracturing can eliminate the influence of spatial island areas and improve the safety of roof water-rich gob-side working face mining.

Reinforcement of bionic trabecular bone scaffolds for bone defect repair using the slime mould algorithm

Bionic trabecular bone scaffolds (Bio-Tb-S), which mimic the human cancellous bone, are widely recognized as the most effective repair material for large bone defects. Nevertheless, in situations with bone defects located in high-stress areas with intricate and varying mechanical environments, the scaffold necessitates reinforcement to withstand the limit stress. Achieving a balance between the “mechanical load-bearing properties, elastic modulus, and permeability” represents a substantial challenge. A scaffold with locally personalized reinforced was proposed based on slime mould algorithm (SMA), called bionic trabecular bone scaffold with slime mould algorithm (Bio-Tb-S-SMA), that is capable of echoing hard tissue characteristics. Additive manufacturing (AM) was utilized to fabricate the scaffold owing to its superior manufacturing flexibility. Compression tests, friction tests and bidirectional fluid–structure interaction experiments to evaluate the mechanical load-bearing properties, service stability, and permeability of scaffold. The results demonstrate that Bio-Tb-S-SMA effectively adapts to the complex in vivo stress environment, exhibiting strong bone-bearing capacity and service stability, while simultaneously retaining excellent permeability. Bio-Tb-S-SMA has broad potential for use as a bone repair material, and the bionic design and bionic reinforcement algorithm inject new vitality into the field of tissue engineering.

A landmark-based geometric morphometric approach to quantify deviations from bilateral symmetry in polyplacophorans

The class Polyplacophora (chitons) represents a dorsoventrally flattened mollusk group that has an oval-shaped body covered with eight overlapping sclerites providing bilateral symmetry. Chitons show abnormalities (teratologies) that are characterized by symmetry deviations between the right and left sides of their bodies. As these deviations do not result in damage that affects vital functions, chitons are able to reach adult stages. In this study, we quantify the asymmetric condition of the species Chiton articulatus using a landmark-based geometric morphometric approach to assess variation in shape and bilateral symmetry. A geometric configuration of 22 landmarks and 50 semi-landmarks was created to evaluate shape variation in abnormal and deformed specimens compared to normal Chiton articulatus specimens. Vectors of change in the body shape configurations of chitons indicate that the greatest change occurs in the anterior part of the body, with less change in the middle and posterior parts. This gives chitons a widened appearance and provides anatomic compensation to restore the bilateral symmetry of the body scleritome. The diverse abnormalities and deformities had little impact on shape variations and confirmed that the coalescence condition is an intermediate step between a normal condition and the abnormal conditions of hypomerism or hypermerism. The low levels of fluctuating asymmetry expressed in C. articulatus indicate that despite living in areas of high stress, such as the rocky intertidal coast, this species maintains stability in its development and shape. Our results can serve as a model for studying bilateral symmetry deviation in polyplacophorans.

Comparative Analysis of Buried Pipe Under Heavy Train Loads

With rapid development of railway transportation and increasing demand of oil and gas in China, the heavy haul train load becomes an important factor that threaten the safe operation of pipe. The mechanical behavior of buried pipe subjected to heavy haul train load was investigated in this study. A finite element model was established to investigate the effect of train load. Finally, the multiple train loads were also discussed. Results show that the high stress area occurs under the train track. In the pipe segment below the track, the top of pipe is under compression and the bottom of pipe is under tension. The cross section of pipe is still circular. The maximum vertical and horizontal displacement are at the top and side of pipe. The maximum von Mises stress, axial strain, and displacement of pipe increase with the increase of train load. Under the multiple train loads, there are two high stress and high strain areas at the top and bottom of pipe. With the increase of multiple train loads, the maximum von Mises stress, axial strain, displacement and ovality increase.

Contrast-Enhanced Ultrasound Combined With 2D Strain Imaging and Histopathological Multimodal Assessment of Carotid Plaque Vulnerability.

The aim of this study was to explore the value of contrast-enhanced ultrasound (CEUS) combined with 2-D strain imaging in evaluating carotid plaque vulnerability and the correlations among CEUS perfusion parameters, strain parameters and histopathological findings in different plaque segments. Patients with carotid artery stenosis who underwent carotid endarterectomy (CEA) at the First Affiliated Hospital of Xinjiang Medical University from September 2020 to June 2021 underwent preoperative carotid artery 2-D ultrasonography and CEUS. The plaques were divided into three segments: the proximal end of the shoulder, central cap and distal end of the shoulder. The peak intensity (PI) value and strain rate parameters of the regions of interest were analyzed. Plaques were divided into a stable group (8 cases) and an unstable group (19 cases). The microvascular density (MVD) and vascular endothelial growth factor (VEGF) expression of each patch in the unstable group were analyzed. The peak strain during the systolic period in each plaque segment in both groups showed the following pattern: proximal end shoulder > distal end shoulder > top (p < 0.05). The PI value for CEUS is also represented. In the unstable group, the PI values of each segment of the plaque were positively correlated with the MVD, near-center PI value and VEGF average optical density value. The average optical density of each segment was positively correlated with the MVD (p < 0.05). There were positive correlations between the PI values of the proximal and distal shoulder and the strain values (p < 0.05), and the MVD value of each segment, VEGF value and strain value were positively correlated (p < 0.05). PI and the pathological tissue components represented by CEUS were positively correlated with the mechanical parameters of the plaque along the long axis. There may be overlap between the high shear stress area of the plaque and the neovascular aggregation area, and the combination of the two has certain significance for assessing the vulnerability of the plaque.

Assessing Transboundary Impacts of Energy-Driven Water Footprint on Scarce Water Resources in China: Catchments under Stress and Mitigation Options.

The energy supply chains operating beyond a region's jurisdiction can exert pressure on the availability of water resources in the local area. In China, however, there is a lack of transboundary assessments that investigate the effects of energy consumption on water stress within and across river basins. In this study, we therefore investigate transboundary impacts on scarce water resources that are induced by energy demands (i.e., electricity, petroleum, coal mining, oil and gas extraction, and gas production). We develop a bottom-up high spatial resolution water inventory and link it to a 2017 multiregional input-output (MRIO) table of China to analyze supply chain scarce water use at provincial and river basin levels. We find that the energy-driven water footprint accounts for 21.6% of national water usage, of which 35.7% is scarce water. Nonelectric power energy sectors contribute to around half of the nation's scarce water transfer. We identify three sets of catchments whose water resources are stressed by energy demand, i.e., (a) from the northern Hai River Basin to the eastern part of the Yellow River Basin and the Huai River Basin, (b) the northern area of the Northwest Rivers, and (c) the developed coastal city clusters in the Yangtze River Basin and the Pearl River Basin. We then evaluate the impacts of eight mitigation options, which may potentially shift around half of the moderate- or high-stress areas in the Hai River Basin and the Northwest Rivers to low to moderate (or even low) stress. We highlight the need for transboundary collaboration to sustain water-constrained energy demand and to develop targeted measures to mitigate stress on water resources within a river basin.

Failed Dental Implant: When Titanium Fractures.

Despite the widespread use of titanium implants in orthopedic and dental surgeries, concerns have recently emerged regarding potential deformations and fractures after osseointegration. In a recent clinical case, a titanium implant fractured after successful osseointegration. This fracture occurred despite the absence of any significant trauma or excessive external force applied to the area. The fracture was attributed to a combination of factors, including abutment design flaws, material fatigue, and biomechanical stress imposed on the implant during functional loading. This raises concerns about the long-term durability and reliability of titanium implants, particularly in high-stress areas such as the posterior region or weight-bearing bones. An image was made with scanning electron microscopy showing the fracture region near the prosthetic platform and highlighting the knowledge that despite their ductility, titanium implants can fracture.

Titanium alloy cannulated screws and biodegrade ceramic nails for treatment of femoral neck fractures: A finite element analysis

BackgroundOur previous studies have demonstrated the mechanical effect of sclerosis around screw paths on the healing of femoral neck fractures (FNF) after internal fixation. Furthermore, we discussed the possibility of using bioceramic nails (BNs) to prevent sclerosis. However, all these studies were conducted under static conditions as the patient was standing on one leg, while the effect of the stress generated during movement is unknown. The purpose of this study was to evaluate the stress and displacement under dynamic stress loading conditions. MethodsTwo types of internal fixation, namely cannulated screws and bioceramic nails, were utilized in conjunction with various finite element models of the femur. These models included the femoral neck fracture healing model, the femoral neck fracture model, and the sclerosis around screws model. The resulting stress and displacement were analyzed by applying the contact forces associated with the most demanding activities during gait, including walking, standing, and knee bending. The present study establishes a comprehensive framework for investigating the biomechanical properties of internal fixation devices in the context of femoral fractures. ResultsThe stress at the top of the femoral head in the sclerotic model was increased by roughly 15 MPa during the knee bend and walking phases and by about 30 MPa during the standing phase compared to the healing model. The area of high stress at the top of the femoral head was increased during the sclerotic model's walking and standing phases. Additionally, the stress distribution throughout the dynamic gait cycle was comparable before and after the removal of internal fixations following the healing of the FNF. The overall stress distribution of the entire fractured femoral model was lower and more evenly distributed in all combinations of internal fixation. Furthermore, the internal fixation stress concentration was lower when more BNs were used. In the fractured model with three cannulated screws (CSs), however, the majority of the stress was concentrated around the ends of the fractures.The maximal stress in the healing model with one CS and two BNs was the highest at all stages of gait over three combinations of internal fixation, and the stress was mainly carried by CS. ConclusionsThe presence of sclerosis around screw paths increases the risk of femoral head necrosis. Removal of CS has little effect on the mechanics of the femur after healing of the FNF. BNs have several advantages over conventional CSs after FNF. Replacing all internal fixations with BNs after the healing of FNF may solve the problem of sclerosis formation around CSs to improve bone reconstruction owing to their bioactivity.