Maximum Principal Stress Distribution Research Articles

Stress distribution on teeth restored with veneers using various incisal preparation designs: A 3D finite element analysis study

Statement of problemThe type of veneer preparation is often chosen according to the patient’s tooth structure and occlusion. Taking biomechanics into account in this decision-making process provides the clinician with more technical information on how to improve the clinical longevity of restorations. However, biomechanical analyses of veneer preparation designs are sparse. PurposeThe purpose of this 3-dimensional (3D) finite element analysis with microcomputed tomography (µCT) data obtained from realistic models was to assess the influence of different preparations for ceramic and composite resin veneers on restoration and resin layer stress distribution. Material and methodsFour replicas of a central incisor were printed and prepared for laminate veneers with 4 different incisal edge designs: shoulder (SH), palatal chamfer (PC), palatal chamfer and oblique fracture involving the distal angle (OF-PC), and palatal chamfer involving horizontal incisal fracture (IF-PC). After fabrication and cementation of the veneers, the restored replicas were assessed with µCT, and 3D finite element models were built. A 100-N load was applied on the palatal surface at 60 and 125 degrees relative to the longitudinal axis. Maximum principal stress and stress distribution on the veneers, cement layer, and tooth structure were calculated and analyzed. ResultsThe SH preparation exhibited better stress distribution than the PC preparation, and the cement layer and the veneer were subjected to lower stress. The IF-PC preparation had better stress distribution than the OF-PC. The shoulder and IF-PC showed higher stress on laminate veneers, but lower stress on the cement layer. Ceramic veneers exhibited lower stress than composite resin veneers. ConclusionsThe different incisal preparations for laminate veneers influenced stress distribution on restorations and on the resin cement layer. The shoulder type preparation showed better stress distribution and the composite resin veneers showed unfavorable results compared with the ceramic veneers.

In silico nonlinear dynamic finite-element analysis for biaxial flexural strength testing of CAD/CAM materials.

The aim of this study was to establish and assess the validity of in silico models of biaxial flexural strength (BFS) tests to reflect in vitro physical properties obtained from two commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic blocks and one CAD/CAM resin composite block. In vitro three-point bending and BFS tests were conducted for three CAD/CAM materials (n = 10): Katana Zirconia ST10 (raw material: super-translucent multilayered zirconia, ST10; Kuraray Noritake Dental, Niigata, Japan), Katana Zirconia HT10 (raw material: highly translucent multilayered zirconia, HT10; Kuraray Noritake Dental), and Katana Avencia N (AN; Kuraray Noritake Dental). Densities, flexural moduli, and fracture strains were obtained from the in vitro three-point bending test and used as an input for an in silico nonlinear finite element analysis. The maximum principal stress (MPS) distribution was obtained from an in silico BFS analysis. The elastic moduli of AN, HT10, and ST10 were 6.513, 40.039, and 32.600 GPa, respectively. The in silico fracture pattern of ST10 observed after the in silico evaluation was similar to the fracture pattern observed after the in vitro testing. The MPS was registered in the center of the tensile surface for all three specimens. The projections of the supporting balls were in the form of a triple asymmetry. The in silico approach established in this study provided an acceptable reflection of in vitro physical properties, and will be useful to assess biaxial flexural properties of CAD/CAM materials without wastage of materials.

Design Optimization of Alloy Wheels Based on a Dynamic Cornering Fatigue Test Using Finite Element Analysis and Multi-Additional Sampling of Efficient Global Optimization

An alloy wheel is generally a symmetrically shaped part integral to a vehicle because its weight and strength can improve driving performance. Therefore, alloy wheel design is essential, and a novel design method should be considered. Currently, the Multi-Additional Sampling Efficient Global Optimization (MAs-EGO) has been proposed and widely implemented in various fields of engineering design. This study employed a surrogate model to maximize Expected Hypervolume Improvement (EHVI) for multi-objectives by increasing multi-sampling per iteration to update a surrogate model and evaluate an optimal point for alloy wheel design. Latin Hypercube Sampling (LHS) was used to generate an initial design of an alloy wheel, including the thickness and width of the spoke wheel. The maximum principal stress according to the dynamic cornering fatigue simulation was then evaluated for risk of failure using Finite Element (FE) analysis. The objectives were to minimize both the principal stress and weight of the symmetric alloy wheel. The Kriging method was used to construct a surrogate model, including a Genetic Algorithm (GA), which was performed to maximize hypervolume improvement to explore the next additional sampling point, and that point was also an optimal point for the process when computation had converged. Finally, FE results were validated through a designed apparatus to confirm the numerical solution. The results exhibit thatMulti-Additional Sampling Efficient Global Optimization can achieve an optimal alloy shape. The maximum principal stress distribution occurs in the spoke area and exhibits a symmetrical pattern around the axis following the cyclic bending load. The optimal design point of the alloy wheel can reduce 20.181% and 3.176% of principal stress and weight, respectively, compared to the initial design. The experimental results are consistent trend in the same direction as FEA results.

Vibration-assisted material damage mechanism: From indentation cracks to scratch cracks

Vibration-assisted grinding is one of the most promising technologies for manufacturing optical components due to its efficiency and quality advantages. However, the damage and crack propagation mechanisms of materials in vibration-assisted grinding are not well understood. In order to elucidate the mechanism of abrasive scratching during vibration-assisted grinding, a kinematic model of vibration scratching was developed. The influence of process parameters on the evolution of vibration scratches to indentation or straight scratches is revealed by displacement metrics and velocity metrics. Indentation, scratch and vibration scratch experiments were performed on quartz glass, and the results showed that the vibration scratch cracks are a combination of indentation cracks and scratch cracks. Vibration scratch cracks change from indentation cracks to scratch cracks as the indenter moves from the entrance to the exit of the workpiece or as the vibration frequency changes from high to low. A vertical vibration scratch stress field model is established for the first time, which reveals that the maximum principal stress and tensile stress distribution is the fundamental cause for inducing the transformation of the vibration scratch cracking system. This model provides a theoretical basis for understanding of the mechanism of material damage and crack propagation during vibration-assisted grinding.

FDEM numerical study of the influence law of geostress on state and pressure of tunnel surrounding rock

Surrounding rock pressure is a crucial parameter in tunnel engineering design, and its calculation is a classic challenge. The surrounding rock pressure is influenced by geostress, but existing calculation methods often do not take into account the effect of geostress. In this paper, finite discrete element method (FDEM) is used to study the design values of tunnel surrounding rock pressure under different geostress fields. Firstly, a set of calibration methods for input parameters of FDEM is summarized based on previous studies. Then, taking a high-speed railway tunnel in IV-level surrounding rock as an example, the excavation-induced failure process of the tunnel under the influence of gravity stress field and geostress field is simulated using the FDEM. By comparing the results with those of the finite element method simulation, the rationality of applying FDEM to the simulation of tunnel excavation is demonstrated. Next, a calculation method of surrounding rock pressure design value based on FDEM is proposed by introducing tunnel displacement criterion, and its validity is verified by comparing with the results of the theoretical formula. Finally, the surrounding rock pressure design values under different geostress are analyzed by using this calculation method. The results show that there are significant differences between the gravity stress field and the geostress field in the maximum principal stress distribution, failure zone form and crack distribution. The geostress directly influences the design value of surrounding rock pressure. As the geostress varies from 4MPa to 12MPa, the corresponding design value increases from 49KPa to 1,288KPa, illustrating a quadratic relationship between them. With the corresponding design support force, the displacement of the surrounding rock is controlled within a reasonable range, ensuring the stability of the tunnel is maintained.

Deciphering phase stress partition and its correlation to mechanical anisotropy of laser powder bed fusion AlSi10Mg

Laser powder bed fusion AlSi10Mg exhibits severe mechanical anisotropy, which hinders its applications in industrial field. In the present work, we investigated the mechanisms of anisotropy in the light of phase stress partition, using traditional crystal plasticity and mechanism-based strain gradient crystal plasticity models. Two representative volume elements of the Al-Si cellular structures, corresponding to 35 ℃ and 200 ℃ build platform temperatures, were built to assess the influences of Al matrix strength and strain gradient on phase stress partition and anisotropy. In addition, the maximum principal stress distribution of the Si-rich network was probed, based on which the potential damage sites and densities were evaluated. The results show that the anisotropic strength and damage both originate from the elongated Si-rich network. According to the comparison between the 35 ℃ and 200 ℃ materials, an increase in Al phase strength can change the phase stress partition and effectively mitigate the anisotropy degree. Moreover, it is revealed that the strain gradient tends to alleviate anisotropy and delay damage evolution. The findings of this work can pave the way to developing high-performance LPBF Al alloys with lower degrees of anisotropy.

A comprehensive study for the effect of sample geometry and lateral pressure on shear fractures using the short core in compression (SCC) method

Shear fractures are common in the rock mass, especially with increasing depth, due to the increase in lateral pressure. Hence, investigating these fractures is crucial for improving the stability and safety of underground structures at greater depths. The Short Core in Compression (SCC) method has recently been used by some researchers to generate shear fractures under mode II loading and initiation due to the ease of sample preparation and lateral pressure application. This study examines the impact of sample geometry and lateral pressure on the formation of shear fractures in rocks, by conducting numerical and experimental investigations on SCC samples. In this paper, the effect of sample shape, notch length, and lateral pressure was evaluated depending on the shear and the maximum principal stress distribution. To the best knowledge of the authors, the impact of these factors has not been sufficiently explored in the literature. Moreover, the mode II stress intensity factor, fracture toughness, and fracture path were investigated. The results provided the stress intensity factor for different geometries of the SCC sample that can be used for many applications in mechanical and geological engineering. Our findings showed that the resulting fracture must be evaluated due to the possibility of crack growth under shear σxy or maximum principal stress σmax, especially for Notch Length/Diameter ≥0.5. Additionally, lateral pressure mainly affects the distribution and magnitude of σmax, such that σmax is inversely proportional to this pressure. The results showed that the SCC sample with Height/Diameter = 2 is preferred because σmax is minimum for this sample shape, which promoted fracture growth under shear stress not tensile stress. Furthermore, as the lateral pressure increases, mode II fracture toughness significantly increases and the number of fragments that spalled off the specimen along the fracture path decreases.

A continuum large-deformation theory for the coupled modeling of polymer–solvent system with application to PV recycling

Nowadays recycling of photovoltaics (PV) using the solvent method is becoming a very hot topic as massive products deployed in the last century have approached the end of their service lifetime. The key problem in the recycling of end-of-life PV modules is the nondestructive recovery of precious silicon wafers for the manufacturing of new products. However, the attempt to comprehensively understand the polymer–solvent system in the PV recycling process is completely lacking. In this work, a thermodynamically consistent large-deformation theory is proposed to model the coupled behavior of this system. The development of continuum theory accounts for the solvent permeation, swelling and elastic deformation, as well as shrinking effects due to the initial crosslinking of ethylene-co-vinyl acetate (EVA). The crosslinking of EVA influences the stiffness of the polymer network, and interacts with the diffusive kinetics of solvents. Also, given the effects of mechanical constraint, the two-way coupling between the EVA deformation and solvent diffusion is established on the basis of thermodynamic arguments. The proposed modeling method is firstly applied to simulate the swelling experiments of cylindrical EVA samples in solvents Toluene, Tetrahydrofuran, and Octane, and good agreement has been achieved between the numerical prediction and available testing data. Then the second example demonstrates the capability of this modeling framework to describe the influences of initial crosslinking and mechanical constraints on the time history evolution of swelling and elastic deformation. Finally, the complete PV laminate in the 3D setting is modeled for the investigation of solvent penetration induced deformation in the silicon cell layer during the PV recycling process, and comparison has been made to showcase the spatial distribution of maximum principal stress of the silicon cell layers in solvents with different solubility parameters and molar volumes. With this computational tool at hand, it is possible to provide guidance to the design of suitable experimental procedures for the structure-intact recovery of silicon wafers in PV recycling with the solvent method.

Numerical Simulation of Deformation and Failure Process of Tunnel Surrounding Rock Based on Different Constitutive Models

Based on five different constitutive models, the progressive failure process of deep hard rock was simulated, and the plastic zone, shear strain increment high-value zone, horizontal displacement, and maximum principal stress distribution of surrounding rock were obtained. The calculation results show that the plastic zone of surrounding rock calculated by MCSS and HBSS models is mainly concentrated in the floor and vault of the cavern, and the sidewall is not damaged. There is no shear zone in the surrounding rock, and the magnitude of horizontal displacement is 10-4. In the L-CWFS model, the hysteresis cohesion of friction strengthening is weakened, and the initial friction angle is 0. The calculated plastic zone runs through the surrounding rock, and the whole section is destroyed. The order of magnitude of the horizontal displacement extremum is 10-3. The MC-HB model simulates the spalling failure of the side wall, and the strain localization of the side wall is not obvious, and no shear band is formed inside the surrounding rock deeply. The N-CWFS-TSS model simulates the buckling failure process of the straight wall plate crack. A shear band is formed at the bottom of the straight wall and penetrates into the interior of the surrounding rock. The strain localization is obvious and the order of magnitude of the shear strain increment is 10-2. The calculation results are consistent with the results of laboratory tests and field observations, and the failure mechanism of the compression-shear-tensile-shear composite in the progressive failure process of the surrounding rock is clarified.

Research on Multifactor Analysis and Quantitative Evaluation Method of Rockburst Risk in Coal Mines

Abstract The prevention of rockbursts is significant to ensure mining safety in deep coal mines. The multifactor analysis and a new quantitative evaluation method for rockbursts in coal mines are proposed in this study. In the aspect of rockburst analysis, a multifactor system of rockburst risk based on the material, stress, and large-scale geological structure is proposed. The factors influencing rockbursts in coal mines are analyzed by numerical simulations. Based on a standard mining model, three comparative models considering the rockburst tendency, high stress, and geological structure are established. The distribution of maximum principal stress and plastic zone during the mining process is compared. The reasons why these three types of factors are liable to trigger rockbursts lie in generating high-stress zones in surrounding rock masses. In the aspect of quantitative evaluation, the monitored microseismic signal is selected as the key indicator, and the daily frequency of microseisms is analyzed. A normal distribution function based on the daily frequency of microseisms is established. The interval of daily frequency of microseisms is set to judge whether the microseismic frequency is abnormal and then determine the rockburst risk of coal mines. Considering the results of multifactor analysis, it is proposed that the monitoring system combining microseisms with stress is the direction to accurately and quantitatively evaluate the rockburst risk in the future. This study makes specific explorations in the quantitative evaluation of rockburst risk in coal mines.

Simulation study on the effect of the initial defect of recycled aggregate concrete based on BFEM

To study the effect of the initial defect on the mechanical properties and failure pattern of recycled aggregate concrete (RAC), several numerical models containing the initial defects were established and simulated under uniaxial compression. The recycled aggregate was simulated as an ellipse geometry, which can be constructed by compressing the circular geometry. The base force element method on the complementary energy principle was applied for the loading condition analysis. In addition, the stress–strain curves, deformation, and crack extension patterns of RAC were explored. Moreover, the maximum principal stress distribution and stress concentration were also investigated. The results demonstrate that the angle and length of the initial defect have a significant effect on the mechanical properties of the RAC. The initial defect interrupts the loading transfer path, forcing it into other continuous regions and forming a new transfer path. In addition, the longer the projection length of the initial defect in the loading direction, the most substantial influence on the mechanical properties, stress transfer, and damage mode.

Finite element analysis of the biomechanical effects of titanium and Cfr-peek additively manufactured subperiosteal jaw implant (AMSJI) on maxilla

The aim of this study is to examine the stresses that will occur under occlusal forces on the cortical bone, spongious bone and the subperiosteal implant systems made of Titanium and%60 Carbon fiber reinforced Polyether ether ketone (PEEK) material. Two different models of subperiosteal implant systems on maxilla made of Titanium and %60 Carbon fiber reinforced Polyether ether ketone (PEEK) material. As a result of vertical and oblique forces, the stress values and distributions on the subperiosteal implant systems and bone were examined. After applying the three different force protocols, von Mises stress, Maximum principal stress and Minimum principal stress values and distribution on the subperiosteal implant body, fixation screws, cortical and spongious bone were analyzed by finite element analysis. In all scenarios, the von Mises values ​​on the Titanium subperiosteal implant system were found to be approximately twice on the 60% carbon fiber reinforced PEEK subperiosteal implant system plates. Subperiosteal implants produced from titanium and carbon fiber reinforced PEEK material exhibited similar stress values on cortical and spongious bone. According to the results of this study, 60% Carbon fiber reinforced PEEK material can be considered as an alternative material to titanium since it exhibits similar biomechanical behavior with titanium subperiosteal implants on cortical and spongious bone. In order to be routinely used as dental subperiosteal implant material, it should be supported by long-term in vivo studies.

Fatigue analysis of high-carbon steel at different environmental temperatures considering the blue brittleness effect

Fully-reversed bending fatigue and impulse excitation tests are performed to investigate the behavior of High Carbon Steel (HCS) during cyclic loading at different environmental temperatures. The evolution of the damping, elastic modulus, and frequency for different operating temperatures ranging from 23°C to 135°C is characterized. The results of the damping are related to the rate of damage accumulation and crack growth―both of which are shown to increase with increasing the environmental temperature. It is shown that specimens tend to become more brittle with increasing of environmental temperature due to the so-called blue brittleness effect, and consequently the fatigue life of the specimens decreases. To gain further insight, a finite element model (FEM) is developed to assess the maximum principal stress distribution. The results corroborate the experimental findings.

On the effect of irregular uterine activity during a vaginal delivery using an electro-chemo-mechanical constitutive model

During a normal vaginal delivery, the muscle cells propagate electrical signals throughout the uterine wall, resulting in uterine contractions. However, uncoordinated uterine activity may disturb the uterine contractions pattern and negatively impact fetal and maternal health. Some of the abnormalities identified by the specialists are excessively short resting intervals and tachysystole. This work aims to investigate the influence of abnormal uterine activity in terms of maximum principal stress distribution and collagen fibers stretch in the uterine tissue during vaginal delivery with (i) excessively short resting intervals without changing the contraction time, and (ii) tachysystole (contraction and reduced resting times). These patterns are compared with a normal uterine contraction pattern. To achieve our aims, a biomechanical model was developed, including finite element models of the uterus and the fetus, and an electro-chemo-mechanical constitutive model. Generally, the excessively short resting intervals exhibit higher average maximum principal stresses during the contraction and resting stages, lower average fibers stretch values in the longitudinal direction and higher stretch in the circumferential direction. On the other hand, the tachysystole exhibit generally lower stress values during the uterine contraction and higher stress values during the resting stages, higher stretch in the longitudinal direction, and lower stretch in the circumferential direction.

Influence of thermal and thermomechanical stimuli on a molar tooth treated with resin-based restorative dental composites

ObjectivesIn-vivo experimental techniques to understand the biomechanical behavior of a restored tooth, under varying oral conditions, is very limited because of the invasive nature of the study and complex tooth geometry structure. Therefore, 3D-Finite element analyses are used to understand the behavior of a restored tooth under varying oral conditions. In this study, the distribution of maximum principal stress (MaxPS) and the location of MaxPS on a restored tooth using six different commercially available dental resin composites under the influence of thermal and thermomechanical stimuli are performed. MethodsAn intact tooth was scanned using µ-CT and segmented to obtain separate geometric models of the tooth, including enamel and dentine. Then, a class II mesial-occlusal-distal (MOD) cavity was constructed for the tooth model. The restored tooth model was further meshed and imported to the commercial Finite Element (FE) software ANSYS. Thermal hot and cold stimuli at 50 °C and 2 °C, respectively, were applied on the occlusal and lingual surface of the tooth model with the tooth’s ambient temperature set at 37 °C. A uniform loading of 400 N was applied on the occlusal surface of the tooth to imitate the masticatory forces during the cyclic thermal stimuli. ResultsThe results of this study showed that the restorative materials with higher thermal conductivity showed a lower temperature gradient between the restoration and enamel, during the application of thermal stimuli, leading to a higher value of MaxPS on the restoration. Moreover, on applying thermal stimuli, the location of MaxPS at the restoration-enamel junction (REJ) changes based on the value of the coefficient of thermal expansion (CTE). The MaxPS distribution on the application of simultaneous thermal and mechanical stimuli was not only dependent on the elastic modulus of restorative materials but also their thermal properties such as the CTE and thermal conductivity. The weakest part of the restoration was at the REJ, as it experienced the peak stress level during the application of thermomechanical stimuli. SignificanceThe findings from this study suggest that restorative materials with lower values of elastic modulus, lower coefficient of thermal expansion and higher values of thermal conductivity result in lower stresses on the restoration. The outcomes from this study also suggest that the thermal and mechanical properties of a restorative material can have a considerable effect on the selection of restorative materials by dental clinicians over conventional restorative materials.

A Fluid-Structure Interaction Simulation of Coal and Gas Outbursts Based on the Interaction between the Gas Pressure and Deformation of a Coal-Rock Mass

Based on the theories of the gas seepage in coal seams and the deformation of the coal-rock medium, the gas seepage field in coal-rock mass is coupled with the deformation field of the coal-rock mass to establish a fluid-structure interaction model for the interaction between coal gas and coal-rock masses. The outburst process in coal-rock masses under the joint action of gas pressure and crustal stress is simulated using the material point method. The simulation results show the changes in gas pressure, velocity distribution, maximum principal stress distribution, and damage distribution during the process of the coal and gas outburst, as well as the movement and accumulation of coal-rock masses after the occurrence of the outburst. It was found that the gas pressure gradient was greatest at the working face after the occurrence of the outburst, the gas pressures and pressure gradients at each location within the coal seam gradually decreased with time, and the damage distribution was essentially the same as the minimum principal stress distribution. The simulation further revealed that the outburst first occurred in the middle of the tunnel excavation face and that the speed at which particles of coal mass were ejected was highest at the center and decreased toward the upper and lower sides. The study provides a scientific basis for enhancing our understanding of the mechanism behind coal and gas outbursts, as well as their prevention and control.

Process design and finite element analysis of multi-station two-roller cassette hot rolling for aluminum alloy 6061 wire

In this paper, a round-oval-round roller cassette wire rolling process of the aluminum alloy 6061 was studied for the process and the roller design evaluation. The elliptic groove of roller was designed for the stand of oval cross-sectional profiles. The billet diameter for this 10- stand rolling process simulation is 20mm. The diameters for the round cross-section profile stands are 16mm,12.8mm,10.2mm,8.2mm, and 6mm, respectively. The forming conditions for the CAE simulation is 400 °C for billet temperature, 0.45 for the constant shear friction factor, 20mm/s for the initial rolling speed. The CAE (Computer Aided Engineering, CAE) results had shown the maximum dimension deviation of the billet is less than 0.25 mm at the location of the roller gap and almost perfect match at the other locations. The maximum principal stress distribution on the cross section had shown a two third area was deformed under the rolling process. The CAE results had demonstrated the proposed process and die design was able to make the smaller wire with good geometrical accuracy without breaking the wire during the rolling process because of the more uniform stress distribution at the cross section of wire.

Splint stiffness and extension effects on a simulated avulsed permanent incisor-A patient-specific finite element analysis.

Splinting is an important procedure after avulsion. However, the role of splint stiffness and extension is not fully understood. The aim of this study was to evaluate the effect of splint stiffness and extensions on the mobility and stress on an injured tooth under physiological biting load. Three-dimensional (3D) finite element models were created from a cone beam computer tomogram of a patient with normal occlusion. An avulsion injury of the right central incisor was created with a 1000N load application on the palatal of the injured tooth, causing increased socket width. Splints made from four materials were tested: 0.9mm diameter wire-composite splint (WCS1), 0.4mm diameter wire-composite splint (WCS2), 1.0mm diameter nylon-composite splint (NCS), and a 2mm high by 0.2mm thick plastic strip composite splint (PSS). Three splint extensions (involving 6, 5, and 3 teeth) were evaluated. Mobility of the avulsed tooth and the maximum principal stress distributions in the adjacent teeth were calculated. The injured incisor tooth mobility was not affected by the splint extensions. The NCS and PSS stabilized the avulsed incisor but allowed, respectively, 10 and 20 times more mobility under horizontal loading than the WCS1, which inhibited most mobility, while the WCS2 allowed double the mobility compared with WCS1. The NCS and PSS allowed more tooth mobility, mainly in the extrusion direction. Splints were 2-3 times more effective in limiting mobility under intrusive loads than extrusive loads. High levels of stress were found at the base of the composite attachments in the adjacent incisors. Splinting an avulsed tooth to one or two teeth bilaterally using a nylon splint or a plastic strip is appropriate for tooth stabilization and should be recommended over the 0.4mm wire-composite splint, while the 0.9mm orthodontic wire is too rigid and not recommended.

Titanium Alloy Gamma Nail versus Biodegradable Magnesium Alloy Bionic Gamma Nail for Treating Intertrochanteric Fractures: A Finite Element Analysis

ObjectiveTo using finite element analysis to investigate the effects of the traditional titanium alloy Gamma nail and a biodegradable magnesium alloy bionic Gamma nail for treating intertrochanteric fractures.MethodsComputed tomography images of an adult male volunteer of appropriate age and in good physical condition were used to establish a three‐dimensional model of the proximal femur. Then, a model of a type 31A1 intertrochanteric fracture of the proximal femur was established, and the traditional titanium alloy Gamma nails and biodegradable magnesium alloy bionic Gamma nails were used for fixation, respectively. The von Mises stress, the maximum principal stress, and the minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.ResultsIn the intact model, the maximum stress was 5.8 MPa, the minimum stress was −11.7 MPa, and the von Mises stress was 11.4 MPa. The maximum principal stress distribution of the cancellous bone in the intact model appears in a position consistent with the growth direction of the principal and secondary tensile zones. After traditional Gamma nail healing, the maximum stress was 32 MPa, the minimum stress was −23.5 MPa, and the von Mises stress was 31.3 MPa. The stress concentration was quite obvious compared with the intact model. It was assumed that the nail would biodegrade completely within 12 months postoperatively. The maximum stress was 18.7 MPa, the minimum stress was −12.6 MPa, and the von Mises stress was 14.0 MPa. For the minimum principal stress, the region of minimum stress value less than −10 MPa was significantly improved compared with the traditional titanium alloy Gamma nail models. Meanwhile, the stress distribution of the bionic Gamma nail model in the proximal femur was closer to that of the intact bone, which significantly reduced the stress concentration of the implant.ConclusionThe biodegradable magnesium alloy bionic Gamma nail implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of postoperative complications associated with traditional internal fixation techniques, and it has promising clinical value in the future.

The torsion test offers a new approach for evaluating CAD/CAM material bonding

This study assessed the validity of torsion test, by comparing it with shear test, in evaluating the bonding of resin composite core after different surface treatments to both zirconia and resin composite CAD/CAM blocks. In total, 108-resin composite core cylinders (3 mm × 3 mm) were prepared and stored in distilled water at 37 °C/48 h. The cylinders were subjected to no-treatment, sandblasting, or surface grinding. Cylinders from each treatment group were then bonded with either zirconia or resin composite CAD/CAM blocks using dual-cure resin cement and stored for 24 h. They were subjected to torsion (rotational speed, 0.25 rpm until failure) or shear (crosshead speed, 1.0 mm/min) tests (n = 9 for each core/block combination in each test). All fractured surfaces were observed by scanning electron microscopy, and the maximum principal stress (MPS) was assessed using finite element analysis (FEA). In the torsion test, the sandblasted composite core and resin CAD/CAM block showed significantly lower bond strength than the other groups (p < 0.05), but the shear test results showed no intergroup differences. While 39.89% of the specimens showed cohesion failures in the torsion test, 55.56% showed adhesion failures in the shear test. FEA demonstrated an even distribution of MPS from the outer edge to the center of the cement layer during the torsion test; however, MPS was unevenly concentrated at the bottom edge of the cement layer during the shear test. The torsion test was better than the shear test in bond testing because of the uniform tensile stress distribution and unidirectional displacement at the bond interface.